PHOTO  CHEMICAL  REACTIONS  OF  THE  HALOGENS 


BY 

JACOB  NEVYAS 

A.  B Swarthmore  College,  1919 


THESIS 

SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 
FOR  THE  DEGREE  OF  MASTER  OF  ARTS  IN  CHEMISTRY 
IN  THE  GRADUATE  SCHOOL  OF  THE 
UNIVERSITY  OF  ILLINOIS, 

1922 


URBANA,  ILLINOIS 


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UNIVERSITY  OF  ILLINOIS 

THE  GRADUATE  SCHOOL 

_ Lj  192 JL 

: I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 

SUPERVISION  BY  JACOB  NEVYAS 

ENTITT.ED  PHOTOCHEMICAL  REACTIONS  OF 

THE  HALOGENS  ^ 

i BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE 

REQUIREMENTS  FOR 

THE  DEGREE  OE  MSTER  OF  ARTS  . 

Mn  Charge  of  Thesis  ; 

of. 

■”  C 

Head  of  Department  1 

Recommendation  concurred  in* 

Committee 

on 

Final  Examination* 

•Required  for  doctor’s  degree  but  not  for  master’s 

<;-2SS98 


CONTENTS. 

I.  INTRODUCTION  1 

II.  HISTORICAL  11 

III.  EXPERDIENTAL 

Part  1. 19 

Part  3. 31 

Part  3,  31 

Part  4 35 

IV.  CONCLUSIONS 37 

V.  ACKNOl^/LEDGMENTS 39 

VI.  BIBLIOGRAPHY  • 4q 

PLATE  I. 34 

PLATE  II. 30 

PLATE  III. 33 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/photochemicalreaOOnevy 


1 


I.  INTRODUCTION. 


Chemical  reactions  which  are  initiated,  accelerated,  or 
retarded  iinder  the  influence  of  radiant  energy  of  tie  visible 
spectrum  or  of  the  ultra-violet  are  given  the  name.  Photo- 
chemical Reactions.  The  most  common  instances  of  photochemical 
activity  are  the  action  of  light  on  the  silver  salts  used  in 
photography  and  the  role  of  sunli^t  in  the  metabolism  of  plant 
life, whereby  the  chlorophyl  in  green  plants  is  enabled  to  build 
up  an  almost  endless  variety  of  complex  sugars  and  starches 
from  the  simple  substances:  water,  oxygen,  and  carbon  dioxide. 

Other  well-known  cases  are  the  fading  of  dyed  fabrics  and 
colored  wall  papers  through  photochemical  oxidation  of  the 
coloring  materials  and  the  darkening  of  li^t  paints  on  surfaces 
exposed  to  strong  sunlight,  Turhere  the  reaction  is  probably  a 
polymerisation  of  the  oil  used  as  the  paint  vehicle.  Photo- 
chemical darkening  or  decomposition  of  organic  substances, 
such  as  aniline,  are  quite  common  while  halogenation  of  organic 
substances  as  in  the  chlorination  of  acetic  acid  and  of  benzenel>2 
in  sunlight  are  widely  used  in  Organic  Chemistry.  Less  known  is 
the  phot obrominat ion  of  toluene  and  xylene  with  the  aid  of  ultra- 
violet llght^.  Other  photochemical  reactions  that  have  been 
extensively  studied  are  the  conversion  of  maleic  acid  into  its 
Geometric  isomer,  fuma^ric  acid^, 


the  polymerisation  of 


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anthracene  to  dianthracene , the  decomposition  of  gaseous 
ammonia^,  and  the  conversion  of  the  trans -compound  of  o(-methyl 
cinnamic  acid  into  the  c is -compound^  under  the  influence  of 
ultra-violet  light. 

In  many  of  these  isomeric  changes  and  polymerisations 
the  reverse  reaction  sets  in  as  soon  as  the  activating  influence 
is  removed  so  that  in  tim.e  the  original  compound  is  reproduced. 
Two  examples  of  interest  in  Inorganic  Chemistry  are  reported. 

An  alcoholic  solution  of  phosphotungstic  acid  on  exposure  to 
sunlight  turns  an  intense  blue*^.  This  is  believed  to  be  due 
to  an  oxidation  of  the  alcohol  to  aldehyde  with  corresponding 
reduction  of  the  acid  to  a blue  compound  of  unknown  composition. 
In  the  dark  this  blue  color  gradually  disappears  and  the  solution 
becomes  thoroughly  white  again,  Lenher®  reports  that  a solution 
of  molybdenum  trioxide  in  that  remarkable  solvent,  selenium 
oxychloride,  turns  to  a deep  indigo-blue  when  exposed  to  strong 
sunlight  or  to  the  electric  arc  for  a few  minutes.  When  this 
blue  solution  is  removed  ftpom  the  li^t  it  gradually  fades  to 
the  pale  yellov;  of  the  original  solution.  Strange  to  say, 
heating  this  blue  solution  gently  also  discharges  the  color. 

On  the  other  hand, many  combinations  or  decompositions  effected 
by  photochemical  means  remain  permanently  in  the  reacted  state 
after  the  source  of  radiant  energy  has  been  removed.  Examples 
of  these  are  the  formation  of  phosgene^  by  the  combination  of 
carbon  monoxide  with  chlorine  and  the  formation  of  hydrogen 
chloride  from  the  elements,  as  well  as  the  organic  halogenations 


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mentioned  above. 

However,  although  the  number  of  known  photochemical 
reactions  is  quite  large  and  is  continually  increasing,  definite 
and  consistent  information  bearing  on  even  the  simpler  photo- 
chemical phenomena  is  notably  lacking  through-out  the  literature* 
The  subject  of  Photochemistry,  itself,  is  too  new  to  have  as 
yet  developed  an'jjtheories  and  explanations  of  photochemical 
reactivity  applicable  to  more  than  a few  isolated  instances. 

The  attempts  that  have  been  made  to  correlate  our  small  store 
of  observed  data  with  the  more  general  laws  of  Physical  Science 
may  be  profitably  considered  here. 

The  earliest  attempt  to  apply  a generalization  to 
reactions  influenced  by  light  was  made  by  Theodor  von  Grotthuss^O 
who  stated  "that  in  a photochemical  reaction  only  those  waves 
which  are  absorbed  by  the  reacting  substances  can  be  chemically 
active"*  This  law  was  later  carefully  investigated  and  apparently 
verified  by  Draper^^  who  studied  the  sensitivity  of  daguerreo- 
type plates  to  various  colors  of  visible  li^t.  Bancroft^^'^® 
in  his  articles  on  the  Electrochemistry  of  Light  has  extended 
Draper’s  work  to  the  study  of  light  sensitivity  of  gelatinized 
photographic  films  which  have  been  coated  with  organic  dyes* 

The  dyes  act  as  optical  sensitizers  and  by  absorbing  light  of 
various  wave  lengths  make  the  films  reactive  to  rays  which  would 
otherwise  be  without  effect.  However,  the  Grotthuss -Draper  Law 
has  but  a limited  application,  many  reactions  going  in  direct 
contradiction  to  it*  Bancroft^^,  himself,  admits  that  "there  is 


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never  an  exact  coincidence  betv/een  the  absorption  bands  of  the 
dyed  films  and  that  portion  of  the  spectriim  to  which  color 
sensitiveness  is  increased.”  Also  in  the  photochemical  oxidation 
of  quinine  with  chromic  acid,  Luther  and  Forbes^^  have  shown 
that  the  maximum  reaction  does  not  necessarily  follow  the  region 
of  maximum  absorption.  Grotthuss^®  considered  that  the  action 
of  a ray  of  light  is  analogous  to  that  of  a voltaic  cell  and 
that  in  a photochemical  process  positive  and  negative  charges 
are  set  up  which  give  rise  to  the  resultant  chemical  action. 
Bancroft  feels  that  his  work  substantiates  this  view  and  says 
that  " the  theory  of  Grotthuss  accounts  for  all  action  of  light 
on  salts”  He  ajso  develops  a theory  of  the  formation  of 

positive  and  negative  ions  by  the  action  of  light  to  explain 
the  halogens t ion  of  organic  hydrocarbons  by  the  use  of  "carriers”. 
That  the  amount  of  reaction  is  proportional  to  the  absorbed 
radiation  was  suggested  by  Draper^^»^^  who  studied  the  photo- 
chemical combination  of  hydrogen  and  chlorine  quantitatively 
and  found  that  the  velocity  of  the  reaction  is  inversely 
proportional  to  the  square  of  the  distance  from  the  source  of 
the  ill\iminatlon  and  therefore  directly  proportional  to  the 
intensity  of  the  inciting  radiation. 

It  is  generally  conceded  that  photochemical  reactions 
are  more  sensitive  to  the  shorter  wave  lengths.  In  their  work 
on  the  oxidation  of  ketoses  and  aldoses  Bertholet  and  Gaudechon^*^ 
state  that  the  ease  of  reaction  is  favored  by  an  increase  in  the 


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5 


frequency  of  vibration  of  the  li^t  and  even  go  so  far  as  to 
postulate  the  hypothesis  that  "an  increase  in  vibrational 
frequency  of  exciting  light  should  have  the  same  effect  on  a 
photochemical  reaction  as  an  increase  in  temperature  on  a 
thermal  reaction", 

Byk^®  regards  the  mechanism  of  photochemical  action  as 
essentially  that  of  a rapidly  alternating  electrolytic  process 
in  which  the  light  energy  is  propagated  in  the  form  of  a rapidly 
alternating  electric  current.  This  is  in  harmony  with  our 
conceptions  of  the  nature  of  light  as  an  electromagnetic 
phenomenon.  He  further  assumes  that  in  a photochemical  reaction 
the  work  performed  against  the  chemical  forces  is  proportional 
to  the  energy  falling  on  the  reacting  system.  With  this  as  a 
basis  he  calculates  from  thermodynamic  reasoning  the  work  done 
in  transforming  one  mole  of  a substance  through  the  influence 
of  radiant  energy^^.  Byk  applied  his  equations  to  the 
polymerisation  of  anthracene  to  dianthracene  and  obtained  a 
fairly  close  agreement  of  theory  with  experiment  for  high 
concentrations  of  anthracene.  For  low  concentrations  of 
anthracene  the  amount  of  light  energy  required  to  transform  one 
mole  was  considerably  higher.  To  account  for  this  discrepancy 
Byk^O  get  forth  his  Electromagnetic  Theory  in  v/hich  he  assumed 
that  light  has  a loosening  effect  on  the  electronic  constituents 
of  the  molecules  which  results  in  the  temporary  formation  of 
positive  and  negative  ions  the  loss  of  an  electron  producing 


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''•■''y*i5j'  ' ff'-  ' '.f'  % ' /S\ 

'km^  Qn  i-ikiipm  x^t^m  tt>  ^ * 

■ -.•1.  ■ '5:  * ^ '■  ' ' ^'.V'’  ‘ , . Ci^si^S; 

•<•*2^0  nJ>*2(. 'itoa  :?xijrcpo  OX*  .«x^X8X4  y;X^^4:9hXiBti<>p 

a t*8 .'  m fi u dw  px  j thrnm^o'tiiopiix  hX4  di^io%  , , 


1 .1  ‘.•:-  ' e . I w ' '■  'fl  ' •'isSpa 

t r*  , ■ ■•:  ' '.^  '■  7 V p 

. ■.f-;  ‘iv;  ':(OXdif'rtc'X 

f.  •■;•  ■ ,.  "'V.  . ix  . ''■  * '.a  a;' 

C-  ■^-'i.t oiifiicr^po'xig^irra,'  «jf.v.*3r4,  e«oX  ^4  -?”'  iJ-.-RJilh’  J^£t«'-'<}vlti>sM5  ^ 

3 , *■  "'v  y'^t  '/.  ' '*'  ' ■•«>'•  ' ■ r«w  ,■  C'71'..i!:..  ..  . J 

■flf4. 


w.->^  ;.AV'  ^ 

■ V,  ...  ■‘”  V -•' 


S ! >' 


6. 

a positive  ion  and  tiie  gain  of  an  electron  producing  a negative 
one.  This  suggests  the  earlier  assumptions  of  Grotthuss . Byk 
then  assumes  that  these  ions  are  in  vibration  and  that  in  a 
photochemical  reaction  some  of  the  incident  radiant  energy  is 
used  up  by  the  ion  in  its  oscillations  before  it  can  collide  and 
react  with  an  oppositely  charged  ion.  In  a concentrated  system 
the  mean  time  between  collisions  of  ionized  molecules  is  small 
so  liiat  the  amount  of  light  energy  converted  to  heat  throu^ 
translatory  motion  may  be  relatively  negligible.  In  a dilute 
system,  however,  the  mean  distance  travelled  by  an  ionized 
molecule  will  be  many  times  larger  and  the  amoimt  of  light  energy 
used  up  to  traverse  space  may  increase  to  an  appreciable 
proportion  of  the  incident  energy.  Byk  was  able  to  get  but  a 
qualitative  idea  of  the  amoiint  of  light  energy  thus  dissipated 
but  he  has  shown  thermodynamically  that  for  very  low  temperatures 
even  in  dilute  systems  this  value  would  be  negligible  and  the 
electronic  assumption  unnecessary^®.  Weigert^^'®^  has  developed 
a set  of  thermodynamic  equations  substantially  equivalent  to 
Byk*s  equations.  He,  however,  rejects  the  Electromagnetic  Theory 
altogether  and  takes  exception  to  Byk's  calculated  values  for 
dilute  systems  in  the  anthracene -dianthracene  reaction  on  the 
grounds  that  the  constants  used  by  Byk  were  not  obtained  from 
truly  representative  experiments®®,  Luther  and  Weigert  ^4,25 
had  studied  the  same  reaction  earlier  and  proposed  a theory  of 
the  formation  of  intermediate  compounds  to  account  for  the  fact 
that  only  about  fifty  percent  of  the  incident  light  energy  was 


> •< 


r 


f'V,"  ?*-' 

. \ -a  ■ f 

,t  - , 3'  f It 

e<g*-J4^arr  ■■  ••  Tlr^rf^onP^  '>iv^  r to 

»■  i kjt  >4^-'r  »i.rtoa' 

^ K ■.■■■*  * 

S<  .•%!  X‘  ^ ^ - ’*'  le-rtOfl  ' 

fcU  . ■ • •►  ■ , - ’Vv  "'  : ^ 

-*i  i *AX/^iftr«xjh  L trt  r/al  ^ 

tdi  — 5*'jS  ‘ ’ P' 


, . X^cr'^T!  r^t^^5tJrai*?r>  a fSl  t^rJA  ^ 'ft 

' r . ' •-  , - ^ " ‘ .H 

T Cf/vv^i^fe  ’'6  «ap‘irJ/rpai;t;J4<>irji><f  acr^ 

»•  ^ \3Tfflrii  .1tivri  Ic  i3o«*  ,0iid!V,C^4tj.pe 

Mnn  H ' .■?/■''  ''K  'Kfifg;  'W 


I 


:avA»f-f  «rt<t : V7?>v  tvw/t: 


j, 


o 

I* 


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■ I- 


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P fji*.t*'{: "'  'C^.  i.fc/i1.*  ^'li-'i.;  *dai^  '>-<v 


1 


te 


'ia'^  'n<.rir  tyr 
■V  Urir-  . ^rf3rtt>‘‘’^*jE‘3''i)ai 
.;  ‘dpi  ^ •.(;  jr‘!.tj(^-  4^* 

• " ■-  . " 1,«  ■ ' ■A.'^V  * 

ft.f4A‘t>!/'',-T  Vif  V -tsp’l  .!ftfU  •nOYf:f^  nfrpgy  ai»rf 

- '•.■  ^-1.,  , J.!TS  \: 

o*.  ’ -;^f»  » i .*'5<?d'  dO' J0^.{ /iWr  rj4/«7^v* 

I '■  wf-V  r./'-Sf'.  ,- 

nt'v/o . .,4  4,1  . 4'« 

;i-<  - ■';•■'  .■  • '■  r.-'  ’■■  ‘■'  * ,¥ 

oXro<:j>A4p]^jf5i'.XS  iicf^y  ,«jr  ,a.^tis4t#J;/p.d 

» . . -■-  - 

•tP'i  ••♦V/  > r. ':3|^,0T\€^C»4J^0P.XP 

■ ' " *'  Ni 


_!  ,,/mU  /X.;  .4.: 

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» "a 


**■: , . . .-  ..  ' ■ " ' ■ ■'  ■’’.  ■■  />.  . ■ . . ' • '•-  y.' 

■ • J*  ■ TO  ^ V ■ ■ ^'"iTl.  * '4*'% 

„ ' :ii,r 

*.  I ■ '2Udl  ..1  V'.  .•  ft'  '■  ^:  •'X  .»'■'*  ' 


;i 


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li* '^  '.' f ' ■ ■■rld^'. 


7. 


chemically  effective.  They  made  a distinction  between  chemically 
absorbed  light  and  thermally  absorbed  light  and  assumed  that  by 
the  absorption  of  light  one  or  more  intermediate  compounds  were 
formed  which  in  turn  absorbed  heat  to  a marked  degree  and  broke 
down  to  give  the  final  reaction  products.  Weigert^^*^*^  supports 
this  view  again  in  opposition  to  Byk’s  Electromagnetic  Theory 
in  citing  his  observations  on  the  photochemical  oxidation  of 
dye  solutions, 

Einstein^®'^^  has  applied  the  principles  of  the  (^uantTom 
Theory  to  explain  the  mechanism  of  photochemical  reactions  with 
a fair  degree  of  success.  He  assumes  that  a reacting  system 
absorbs  energy  in  integral  units  corresponding  to  Planck* s 
conception  of  quanta  and  postulates  the  Einstein  Law  of  the 

Photochemical  Equivalent  as  follows:  For  the  decomposition  of 

gram 

^equivalent  of  a reacting  substance  through  photochemical 
means  an  amount  of  radiant  energy  equal  to  Whv  must  be  absorbed. 
Here : 

N - Avagadro*s  Number 
h = The  Planck  Constant 

y'  - The  characteristic  vibrational  frequency  of 
the  absorbed  radiation. 

According  to  Stark  ^ the  primary  reaction  in  a photochemical 

process  is  always  the  liberation  of  an  electron  from  a molecule. 
31 

Millikan  finds  that  in  the  case  of  a metal  the  work  necessary 

to  displace  an  electron  from  its  molecule  is  equal  to  hf^,  where 

l^in  this  case  is  equal  to  the  frequency  of  vibration  of  the 
light  which^acting . on  the  metal is  just  able  to  dislodge  the 


4 


” '•  ■ « T 


: I L-’\  ■"  •' ' • ■ . JW  "r.  ■ ^> 

’■■-  ■ _.  ■...,  fc  ..  U.f  ■ 


t/vir^r  . t.iii 

'*  ' 4 , T'i  ' 


^ 'fc  £4 ‘•wiri'do 


V «s 


» 


..'1‘iyru.'*  ..x-.',  f*.'x  ii'jtrS;  /rl  ‘ ® 

^.to  r- -'j' . ; u;-.' ©di  nc  ■>  v '!»-  ,/*'<^r  * 

f . ■-  ^ ■ 7 ‘ - 1 ' ■’  - • - ■ , . 

, • , ,'C  .*  -W  V 


..Ano'^T)P/ovi'.  IwM 

I^t'  '^-r  - ' •’■■ 


* t ‘S  ’ f 

,.^.  * r.jT^jW<fben'ro:>  ■ f ■■  • 'UV'tSU**^  ^ 

'•'fv  3C‘,  iSr^^vff.'  •'fti.i  '.  a4r>  *3c-, 


*;a . r. ^ t . .- ..  .>'.^I;  ;tKr , tcv ; . : iji ^4 1 L*t^i 0 ftit: t4f\ 
X-99t7Z.r-  1U  I -•  « X^ 


f ' » I 


w r , 


C - ''  ■^'  ■■■  ' V S' 


■■’■'  V 


I 


7 ■ ^ 

rf- ij  -‘- 


■('t-K 


m 


• rrr- 


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' ‘lo  \:tJj.vi'|Tt4»''i  tB,"*x3:  fr^fa^v 


tfl' 


. .L'jjAeXoBT  t W 

• A ‘3?^^  4t,C0‘. 


•^uasClr,  H^, 


..T.’il 


> 


srV'  ^ 

i >«'  7ki  «' .1 


8 


electron,  itself.  It  is  possible  that  this  expression  may  also 
apply  to  non-metals  and  compounds  and  that  the  difference  between 
Einstein’s  /lyand  Millikan's  /rv^may  be  the  energy  with  which  the 
electron  leaves  the  molecule  when  the  latter  is  activated  by 
light.  Warburg  has  tested  the  Einstein  Law  and  foimd  that  it 
applies  within  reasonable  limits  to  the  formation  of  ozone^^*^^ 
and  the  decomposition  of  gaseous  ammonia^^»25  i,y  ultra-violet 
light.  However,  the  large  majority  of  photochemical  reactions 
give  experimental  values  for  the  absorbed  energy  per  mole  of 
reacted  product  which  fail  signally  to  agree  with  the  Law  of  the 
Photochemical  Equivalent,  Such  reactiona  are  the  combination 
of  chlorine  with  hydrogen^^,  the  hydrolysis  of  chloroplatinic 
acid^*^,  the  decomposition  of  water  vapor^®,  and  the  hydrolysis 
of  acetone^^.  In  this  last  reaction,  Henri  and  Wurmser  report 
that  the  energy  used  was  onl^  about  one  percent  of  that  required 
by  the  Einstein  Law.  Bodenstein^®  discusses  at  some  length  the 
amounts  of  radiant  energy  absorbed  in  a large  number  of  photo- 
chemical reactions  in  relation  to  the  amount  of  products  realized. 
It  should  be  pointed  out  here  that  Einstein's  Law  states  merely 
that  for  a given  amoimt  of  reacted  products  a definite  quantity 
of  radiation  is  absorbed.  Further  than  that  it  says  nothing 
concerning  the  conditions  under  which  a photochemical  reaction 
is  carried  out;  neither  does  it  take  into  account  the  possibility 
of  the  reaction  products  undergoing  further  change  and  entering 
into  additional  reactions  after  the  influence  of  the  exciting 
light  has  made  itself  felt.  Light  reactions  are  generally 
complex  and  many  of  them  probably  consist  of  a number  of  distinct 


'■’-^  /f^»:'.  ' m r " 

^ .9  ,. 

, ?•  '■,.  ?' 

• :•.«  '1t^i.t.•6-!>  f/;;o  t tr^  .ajiSi^; 


■f.  ■?•  .*  •Hi»’' 
^ *' 


*(J- 


itJL  .tXci^  U ,-jb»xi4>^_->.  ,,. 

' ',  ' • '"'  cw-'^  ■ '''’  *!^ 

4^*f,’  A:'Kff  •tv^I/’'  .-.  ,;  I\»ftlsi^i',r;  i«r^'  hX#^%^ic4t  6 J 


ktj.  i,ir.>r.  -r^i  'iv-’T^c  ' . ^ aiT.  i J5n;»  i>i?7vsv«|r^.t7  ft 

nPJt  'j  ^ 

■^*.^  .»■  i Ur  VJBn';jrH 


I 

i 


• ll. 


‘ 1 


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‘■•^  *'•  .1.  .:,  'l4  fk-i 


i.f--.'", 


X C XM  bafi  )(A  « ’ : ’ 

* i ^ ff  ! . 

^V'  2ht‘  ‘*»  --'■.•■yjai  «£t:  ij\^  ^ 

► '*  ',  . v*V>ir^ 

J*,"  o| 

■•  • ‘‘^/fjpr-r.  3/fo^i/i|  it  ■<••■  ■"*>  -iiicSV^'  JS*'jSf'^ 

* ,*'»'  * i^‘  K'l .fr ',' 

, .’'  » i-  „ . * ■’  " 


* ij,  X ^18*jt‘j:.i^B°  ■ 


f ^:^;i  i -Titjcf  - Vi 


I j ..  drii?rir 


> tio 


MUan  > tv 


’ ‘»ti‘  iHiY'  - AV 


.•'  s 


H 


' ' ' ' 


* ''  ‘ ’ ^ , "^  foi/rv  ne-)aif  i j 


gL*?‘^X0T:  V -j  ‘ '.-A  -xc-^tfw  I j 

I ‘ — '^98 

-j* 

^ -wtff 

■ sr.-r;  ,‘i^'t^:  <<.«*  ■•w>Bift^  ®^fjr##««i,M,  .w»r 


' • _ - , i • ’ ■ >.  ■^'  v:'^^  . ■ 

■j  X"*  • '-  xTrjirjfl:.-  - ” 


9U 

■^k 


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. > 


'•*’  *"•  ji'/'t.o  »„;!ifa!»'‘ 


•*.  4.  ', 


itsfoasQ^ 


ii^V4-.  ■••V ^’®L  ■■  .•*  ■ ll : 


■:  I!  >mvmn»ti 


9 


processes  so  closely  associated  with  the  initial  photochemical 
effect  as  to  he  impossible  of  separate  study  and  Identification, 

A proper  judgment  of  the  value  of  the  Law  of  the  Photochemical 
Equivalent  is,  therefore,  made  exceedingly  difficult.  It  seems 
quite  possible  that  with  closer  study  of  photochemical  phenomena 
leading  to  a clearer  conception  of  the  relation  of  t he  effects 
due  to  light  as  opposed  to  those  due  purely  to  thermal  and 
other  conditions  that  the  Einstein  Law  might  prove  of  much 
greater  applicability. 

That  photochemical  phenomena  are  of  more  general 
occurence  than  is  commonly  supposed  is  the  contention  of  several 
workers  in  the  field  of  chemical  activity.  Trautz^^  has 
advanced  the  idea  that  in  order  to  take  part  in  a chemical 
reaction  a molecule  must  be  in  an  activated  state.  Based  on 
the  theory  of  the  existence  of  activated  and  unactivated 
molecules,  Arrhenius^  has  developed  an  equation  for  chemical 
reaction  similar  to  the  van’t  Hoff  equation: 

d In  K _ E 
dT  R? 

in  which  K represents  the  equilibrium  constant  for  the  reaction 
between  activated  and  unactivated  molecules  of  the  same  species 
and  E represents  the  quantity  "heat  of  activation"  instead  of 
the  usual  term  "heat  of  reaction".  Perrin^^  puts  forth  the 
hypothesis  that  the  action  of  light  plays  an  essential  part  in 
all  chemical  processes  while  Kruger^"^  even  assumes  that 
phenomena  such  as  solution,  solution  pressure  of  metals,  and 


^ t: 


'•  ’ 'Si  ' 

(i  fxk  ’ ■ C t K f>l  ^ <’  <5  j^ocnS Wf  ' 

^ " '''  '•  'i  " V ^ it"  ’ ■ 

■f  '0  WAi  cii\^ 

«as^r  ,^:  ..,  iir 

i.  . .. 


HStS^C  4‘. 

a*  V ^ « «»  1 

C ' '. ' * 

•■;•  .-:■  .../  - 

’V  '■^* 

R 

4rr.-r- 

iO  ^••v‘ 

Ai 


r;  t 


;.r  ••■.•* 
■:>  mi 


. - v^ W 


, ^ . . ? ,>  . ■ :^  •.*;  , 

&|  *‘-  . H - I^T  * ^ ^ *‘‘  * * 

I < -^jw^spc  ‘:n  J»/Vdf-tc<«^..';i  rv<r,‘,:’ 430  

' ■ i ' j - ^ l^iliHB^^''^  ■' 

Jr.,,,.  , . ',•  ..-I;  ,jc;'^.,dji-  «i' f^»c4'(fc. , :'j(tiL^i3^'.  it  a^  iwiTSoFo 

' '?S,... .......  .',  '.,  ■■."^"^.t': ,; 


l)'  -.  ---■;  7 r-i 

|r  , ■'  - ■ i •«'■«•#  Oj»  t'J.'^'^  'lao* 

HF  Vj5  t .)£  . '.*4itv  ■w  iivl^loa  iM  -rl  fl/i  ’..-(iija 


v.JL.sr j»  _ St  ^p ■,»&'*( i^^£- : .-^  ^ M, 

1.-  -.t/:  a/  . 

‘ ^ « a.  ^ « !..  1 -V  fV.  ,-•■  ..a#  “ 


i96i 


4i< 


^ ~ # i' ''  '■  SpjBjS 

'•  t^iii ■!>:■**('&  or 

■Dr.-  ,_^'.  , -'  ■■-* 

f »*«  ^ 

\a 


nJt 


*- 

*J  - • -*-# 


eiitf  ciil*idX  2p.'U:4W'^^ ■ 

' -■’‘■•'f'.'  ' Vo  “ 'te'*''  ' ''  ’ *'  ■'  ' ‘ "'*:  jy'  ■ " M 

.i  i^(  ;.i«t^w»VVi«:'.,v'Jt'<i.r^jiX 

V>  : 'v  ' ' ' ‘ ' r.  ' ’’^  D '5 

• ■=•'  ■J' .y . . .1 'r  '‘»>‘W>,  -'i  ■ '■■«•  Tr^Jla 

. «X4  »«‘,7  W 

> 7.  -w  ' -rtJ  ■■**  ‘f  ■..-  ‘ ^ 


10 


electrolytic  dissociation  may  be  explained  on  the  basis  of  the 
absorption  of  energy  in  the  form  of  radiation.  Following  the 
work  of  these  men  and  several  others  W.  C,  Me,  Lewis"^^  suggests 
the  theory  that  catalysis  is  essentially  a radiation  phenomenon 
consisting  in  the  activation  of  the  reacting  substances  by  the 
absorption  of  one  quantum  (hV)  of  energy  per  molecule.  He 
assumes  that  ordinary  thermal  reactions  are  in  reality  photo- 
chemical processes  activated  by  the  long  wave  lengths  of  the 
infra-red  region  and  that  the  infra-red  radiation,  which  appears 
to  us  as  heat,  is  emitted  in  quanta  by  the  catalyst  and  absorbed 
by  lthe  reacting  substancesf^  Daniels  and  Johnston^*^  support 
this  view  in  discussing  their  work  on  the  photochemical 
decomposition  of  nitrogen  pentoxide  by  stating  that  " there  is 
no  fundamental  difference  between  the  mechanism  of  photochemical 
and  thermal  action",  Langmuir^®  hov/ever  feels  that  the 
radiation  hypothesis  is  not  justified.  He  bases  his  objections 
in  part  on  the  fact  that  in  the  dissociation  of  phosphine  at  948° 
Centigrade  the  amount  of  energy  in  the  form  of  infra-red 
radiation  that  could  be  possibly  supplied  by  even  a perfect  black 
body  at  this  temperature  is  millions  of  times  too  small  to 
account  for  the  observed  heat  of  dissociation.  As  an  alternative, 
he  offers  the  hypothesis  that  the  energy  of  activation  is  obtained 
at  the  expense  of  the  internal  energy  of  the  molecules. 


'(■  I ! D ^ n 


,l 


SiriiTiyt 


™ ,;;*T 


< •«■  ^JKrnlYU.  ■.&.  ■-•)  <ifV^JCnygW^->inT.r1l 

,3iM  . : 

‘ ’«*'•  '*  5c  -.  fi 

In'  ‘ c ^ ' \ . *A‘  /'j,  ■,’  ,?  v^'  HHir'"' 


f<M  ^ ‘ ' V ■ * ■s‘^1  '^'7'  ‘ '■’ 

, 4dor<-wr,r.'^^47 a »^i\4J!flrfi<^u-<s/ vtCfnil-^ 

_,  . ■'  ‘^  ’:,'  ■ ’ , ^fi^' ■ ’'.  ^^r,■ 

li  >1  I .4  ^ irn/iT  ^ A^.  .r'M  1^-4  Mw  ik  nt.  jiT4rV.  m k'  . «<.  IkX  J.  4 


Ti>it^Ci'<oa^f*i  D>.  • 'ijjp  ;».  /i/iOp  r.  i 

B--  I ■ *“*  it  ' ' 1 '■  ^ If, . * . * '*  ' ■ i a I ;j|-  . 


iijnSu  t^dtit  '^lq  u I ti6 


(-4:  «9i  / finar'ii' 

*1  t:  V U 


la  cl  ,<*>2crrJ^,”  x<i  ^usrSc^^ 

( *U''  r.i  Uitrivenn  .,c^ 


i}-'l 


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"■■"  ft-  ' '*  ' ■ ',  . . '.  ..  IS 

fii^e  e»ni/4i^ia^  jirs  iiJ:' ;ia4J 


■-ti  .,  i » , '-ar  ■ Mv  .(•“ 


J 3vvir;(»i|,  ji, 

■t  ‘ ’ . , • '.  • i ■ ■"  ' - *T.  i <>i|&  • - ' ■ ■'  2 

<};^  IXiJfib: ,cit>i ^ f^spa.a' iu'toiXiiai  -14rl>  J 


'M. 


Vy  ^■ 


; \'T, 

k ‘ 


11. 


II.  HISTORICAL. 


The  purpose  of  this  research  was  to  study  the  action  of 
the  halogens,  bromine  and  iodine,  on  hydrogen  under  varying 
conditions  of  temperature  and  illumination  and  to  determine,  if 
possible,  whether  the  resultant  formation  of  the  hydrogen 
halides  is  to  be  regarded  (1)  as  a purely  thermal  reaction,  (2) 
as  a true  photochemical  reaction  in  which  temperature  conditions 
play  but  a negligible  part,  or  (3)  as  a composite  reaction  in 
which  both  thermal  and  photochemical  factors  enter  simultaneously 
in  such  a manner  that  the  presence  of  one  factor  influences 
materially  the  effect  produced  by  the  other.  There  seems  to 
be  less  consistency  in  the  literature  regarding  the  action  of 
these  two  halogens  than  is  the  case  with  their  two  more  negative 
allies,  fluorine  and  chlorine.  It  is  well  known  that  fluorine 
combines  explosively  on  contact  with  cold  hydrogen  in  the  dark^^ 
so  that  this  element  offers  no  ready  field  for  photochemical  or 
thermal  investigation.  The  action  of  chlorine  with  hydrogen 
at  ordinary  temperatures  is  noticeably  influenced  by  the  intensity 
and  frequency  of  the  light  that  is  allowed  to  fall  on  the 
mixture.  In  the  dark  there  is  practically  no  combination  even 
over  a long  period  of  time;  in  diffuse  sunlight  the  action  is 
moderate;  in  bright  sunlight  the  action  becomes  very  rapid  and 
can  be  made  explosive;  while  in  ultra-violet  light  the  mixture 
combines  immediately  with  explosive  violence.  That  temperature 


'r  V'W^  mmm^'  . ,‘r^-'.,  t! 

fv  ' ■'•  , 


■i.? 


, V'  t 

. i^*;,3  I .1  o't  1 1 4 .:i  ...ii: 


A?.  ;' 

•^1*  -i 


■ "*'■  * * ',  • .7 


\ 


^.  . ■ ^***  .■  >.  . ‘ ,-  ^ . . *'*  ^'*TJ»» 


.1  .e?ri:uj:-.‘.:-5  f « rflviiijti it  f>.T44 -4ATji 

' * ,f'  •'/■^^‘  ";  ^ •*  ' 'i  A v,_^fK.t|' 

. . 4W?<nt  i:i'  o*^  .f -.Tte  , ‘mk^ihA^i  •fw.j-  , 'iS^lmiiii 


1 


(S';  t*t<)t-^:3/ (W  fl  uiv 


i:l  e {0; 

® t *4'  -■  ',  » ^ ^ 'j  '<■  ■' 

..  I *iOAf9c»3. 

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*><?  n-^  it(f t£>y^Sle^  CW  *%?  "^«>.«45aianic-5'''| 


5 !>-.^ 


|4f‘-’X''^-»vd/t  ^,\..'  aw^  'Xt,s4;t  i:iii.  9eao;trri*/  ei'jisDaifi^ 

_a^xX^t$^:%  lZ*^u  ;4  iX.-, ’■ wX«fo 

V 


linutfy .tSLi  j Jt  ; It?  • ;•  x/> uilw 


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' ■PJ  ’ . 


%■  ' 


I ’ (-*i^>  ,o4^tx/ijXoi 


^.--  ' -^■ao  rc-n  #' 


. A'  ,•  mA:A\'.s^  ■ w^ir  ■ ■ >,‘  ' ‘‘■ 

Qfit  , fi I < .TO 


I ‘A  •*  '•  w '7^*  jff* , ' ’’•.'j  ''^**3?  ^, '' ' ' jf  .'\j  h "^''.  . jd  ,‘ , 

t4d  ■ fxiilitr^‘4tatitt’  -'^.VAi 


|;'  ‘ " ""  '■■' 
^'■;v 


(I. 


(»lfc\t.  f J;.  ‘ 


7ii/ 


•'M 


KW/ 


;/•■  'T' 


w 


12 


may  have  some  effect  on  the  sensitivity  of  chlorine  to  light  is 
suggested  by  an  early  article  of  Amato'^^  who  claims  that  there 
is  no  combination  of  hydrogen  with  chlorine  in  the  sunlight  at 
a temperature  of  -12°  Centigrade,  There  is  no  later  con- 
firmation of  this  observation.  It  has  been  shown  that  the 
photochemical  combination  of  hydrogen  and  chlorine  does  not 
take  place  in  accordance  with  the  Einstein  Law  of  the  Photochem- 

£>!  RO 

ical  Equivalent  , Bodenstein  has  calculated  that  as  many 
as  10  molecules  of  chlorine  are  brought  into  combination  by 
one  quantum  of  light  energy.  There  have  been  several  theories 
put  forth  to  explain  this  high  activity  of  chlorine,  Nernst^® 
suggests  that  the  chlorine  molecule  is  split  up  into  uncharged 
chlorine  atoms  by  the  action  of  light  and  that  these  atoms  being 
hi^ly  reactive  are  able  to  disrupt  the  hydrogen  molecule  with 
the  formation  of  one  molecule  of  hydrogen  chloride  and  the 
liberation  of  a considerable  quantity  of  heat  energy.  The 
remaining  hydrogen  atom  is  then  able  to  disrupt  a passive  chlorine 
molecule  with  the  accompanying  formation  of  more  hydrogen  chloride 
and  the  liberation  of  an  additional  quantity  of  heat.  This 
latter  reaction  in  t\irn  gives  rise  to  an  additional  activated 
chlorine  atom  so  that  the  process  gives  the  impression  of  being 
an  unending  chain  of  reactions  which  once  initiated  continues 
without  further  addition  of  energy  from  the  out-side  till  one 
of  the  reacting  constituents  is  either  entirely  removed  or 
rendered  so  low  in  concentration  as  to  reduce  the  velocity  of 
combination  practically  to  zero,  Nernst  formulates  this 


reaction  as  follows; 


l,U  fk 


, ' ■'’ijA' Vf '■’ '^i^'TyT«ft 

‘ nt  l^u  ;•  :i;^i’#'‘Jjl*o.  'C'  7llvLtiUtt#*i^.J(jlXf  CQteftf 


, /rOlSui^-  . f * 


'«rf« 


•f  .fk-^ 


tkYltCf  r. 


y »#<■.■  P;  2 i 

‘ 'j*  *t^^'  _ '" 

Xoa  -••-'O;  r.^t  \t  -*C'i4snii4l«cjp 

he-  . ■ ■■  ^ " r.-  't  ' ', 

; • -,.1*;  i .ij  al^^iualSa*iX;>'  'I'vX*.  ?^‘RO«^Ooc '»■  f<i 

f t^i  j>r  ♦>*«  *4  ♦‘.-•^t-v.  l»oA  rK  > •' 

1 li  . ■.  ' ' ;■'  ■.  '■  !•..  fi,  ■'’  ’ " It  ■ — ' 

»■’  yr-*  £ti.‘i  . Jj^iri-e  Vfjl  <?«d^XiIo  lo 

V,  ■^..  , ■'  ■■.iljl>^  - 

-vna  ;sv«d  ipniwif'  Ito 

•■''-c  eo  To  ’i;:: 

*'*  ■(  ..  .•.vii^ 


*•  > ■» 


J, X <iu  jUm  -i  (^xi^hun  pi’^ 

■,  ‘ ..';T  . ,.  , ’ ■■  ..k/^ 

" rlvM  <«: iwu«  4^  tl- 


) - --  ..  -i  ^ ' X«  ”»4  St’ 

. jdJi«  ^ n.^:'tvrvn  od'  oi<»  n«1Ui'-  t4%i4j 


iitffA 


• &;  - ': '73  ' vlt<^iip.iieria'trj.Ti<  «*^u-odlQ(a  :=fiif>  1^/ 

Uit  .t  I'  .A  jMf}d  o xcldftrt?yj>  aIdg'if»J!>X<&rroA  ^ 

ly-  . ?fV  i:  ‘ r ;qi/-ii'lu  oXdi*’ nfluXX' 

' ' ■•  4^2^^  -' V '' ,’x»  '”'*“.ta  ■'  'J!^‘'"’'J 

•to  4>fsc«  '5':. 


SLJ  ^ ‘ ' * t ■*■  ^ "*  ' **  1 1 ^ Vv 

J_J  A:  Hi  ,pii%  titry/f 


•'  f V *"i^.  . ' .Wi 


- ^ ,i,  -;  j] 

^;«p?y  ? 'tfi.'  ^^atyjyjigig^ 


(1) 

(2) 

(3) 


13 


Gig  = Cl  + Cl 

Cl  + Hg  =HC1  -f  II  + 25,000  cal* 

H i Clg=HCl  4 Cl  f 19,000  cal. 

Bodenstein^^  assumes  that  the  action  of  one  quantum  of 
radiant  energy  on  a mixture  of  hydrogen  and  chlorine  is  to  first 
dislodge  an  electron  from  the  chlorine  molecule  leaving  a 
positive  residue  which  immediately  reacts  with  hydrogen  to  form 
hydrogen  chloride.  He  calls  this  the  "primary"  light  reaction 
but  does  not  go  into  any  explanation  as  to  how  the  positive 
charge  on  the  chlorine  residue  is  neutralized.  The  "secondary" 
reaction,  which  he  regards  as  the  more  important  part  of  the 
process,  results  from  the  attachment  of  the  free  electrons  to 
passive  chlorine  molecules.  The  chlorine  molecules  thereby  _ 
become  activated  and  react  with  the  hydrogen  molecules  present 
with  the  formation  of  hydrogen  chloride  and  the  re-liberation 
of  the  electrons.  The  electrons  in  turn  go  through  another 
cycle  in  an  endless  sequence  till  the  reaction  is  either 
completed  or  has  reached  a point  of  stable  equilibrium. 

Bodenstein  represents  his  theory  by  means  of  the  equations; 


(1) 

Cl2 

+ 

Light 

(2) 

01 
1 — 1 
o 

+ 

e 

- Clg- 

(3) 

Clg 

+ 

H2 

= 2 HCl  + © 

The  representation  of  the  photochemical  activity  of 
chlorine  as  taking  place  by  the  formation  of  various  positively 


'VTl 


./>i 


,«: 


■>"\r 


I.  C ''"#*  \\  ,.^o 

^ V-  : \ ' _A“'i 


■V 


. . i 


■y'. 

) 


J m : ‘ 

I.  t ..'  ',  ■ T '>♦■.. 


” -.S-^-?  ’ 'S 


V 4.X'.  k :DH^f,iSJlS,  i ■■4. 

iV  ?» 


■4^-"  ' 4 iPf--  , '"  ' 

> O.rjrt? 'vt'--  !LClr'>/  i'Pt^WC^WLi5.*^i|'ij4,38Jt^^ 


j^%fl  *>t  *--i  c ^i■^VIli'0' 

5^  ■ ■ ■■  . ;.-  ‘ -t  ■’  . ': 


■■  « . ;«  '*'  * ■ V^'  •■'  ' ^ "A  7C  V ■'”% 


**  sV’j  ''.■p,4Wl;i.|’  m'tdi-isXUft  -r,^  . 

' ■ ■ *•■  ■ ’..r  .■»  ■ 


i!)  HI  / ..  (/.  : - j“.  -J  > 


u ,. 


ol’  «. 


^ .-  ■ ■ -■«»  . .-  " V'A‘' 

W’'  v.^,6n " ^.v  5fl 


44  ^ T*  'f  I 

Em'-"'"'-*'  ■'  ' ‘ '■■  •,■-’■''*  " 

'Me;  r‘^r-r*v|fvA'tV  _ci.j.!it.' 

, -¥;i^i4S>tyV  ,•  cy^  ordfi  ' 4f^,;  ' 

f^:  ^ «•  ■'  . ■ ■ ^ 

-/  >•■  ■ •'. I , ’’f'  . ‘ ';  , '.  ■ ® ',■*/.■  •>/♦*<•  ‘•ld|r>j 

is,'  ♦' 

. . .:  . •' ;‘  '-y" 

G>'v^  xw , 4 ’ 


.! 


. ^i-r 


St' 


* 's'?*  • 


f « ‘7. 

I %■ 


■ -V 


14. 

and  negatively  charged  particles  through  the  liberation  or 

attachment  of  electrons  appeals  to  us  because  of  our  present-day 

development  of  the  electronic  nature  of  matter  as  well  as  because 

effect 

of  its  analogy  to  the  photo-electric^^in  metals.  However,  there 
is  a serious  objection  to  this  sort  of  an  explanation  in  the 
minds  of  some  workers  in  view  of  the  fact  that  we  have  at  present 
no  evidence  of  ionization  taking  place  in  a strongly  illuminated 
system  of  pure  chlorine  or  of  any  mixture  of  chlorine  and 
hydrogen^^,  Gohring^^  has  studied  the  above  reaction  and 
subjected  both  Nernst's  and  Bodenstein's  views  to  careful 
analysis.  He  lists  eighteen  possible  reactions  which  might 
occur  in  the  photochemical  interaction  of  hydrogen  and  chlorine 
on  the  assumption  that  the  chlorine  is  activated  by  light  to 
the  forms;  Cl,  Clg,  CI5.  These  active  radicals  may  then  react 
with  hydrogen  molecules  (Hg)  to  form  the  appropriate  amounts  of 
hydrogen  chloride  and  hydrogen  atoms  (H),  or  of  hydrogen  chloride 
and  chlorine  atoms  (Cl);  or  the  various  species  of  chlorine 
radicals  may  react  among  themselves  thus  neutralizing  some  of 
their  activation  and  generally  changing  the  relative  amounts 
of  each  species  present;  or,  finally,  each  species  may  react 
with  the  hydrogen  atom  previously  formed  yielding  hydrogen 
chloride  and  a lower  species  of  chlorine  radical.  Gohring 
inclines  to  a choice  of  Nernst*s  ideas  and  to  the  theory  of  the 
formation  of  activated  Cl^  molecules  to  best  explain  the 
mechanism  of  the  whole  process.  However,  he  admits  that  the 
solution  of  the  problem  is  still  far  from  completion  and  that 
much  additional  evidence  from  a study  of  other  types  of  reactions 


10  rx,'s>Y^<iu  •jAfV 

* '■■  l*'^  ‘ » '■  <*'^  . '*'''  ' 

;^*»D '^'^V4itv«c3 

. ' « ■ * ’ V-  ■;♦'  ' -"'  ‘ ^'  ■ '-^  '■■y~:  f 


^i. 


'J) 


:■  to  *^10.:;  0^: 

: . , , ^.’  ■ ’,^1  if  ■•••.•„>'■  ■»•.  ^ 

jii  *VJI1  flOi,^:il.ir.:  'sc*''*ti<^«i)jy«',«<ri 


■ I; 

j' 

! 


f\-‘'^^Ui-^  -jaiiMHu  ^ vlidfo;. 


; S' 


!^’  'ifc-t  wii^Mr  - •«»c4i  ailtf  J»«_"x.t.ii-.  Aij(  ■S^^uiTj;}^  '^K  ^^o'.'fWi 


f .7  ’iv^l  V.  « ' rj  ft 


' vttt^VK 

'.“  ^Ct’jvvo '*&>  *xoi- rt/t  “ial^co 

'■  ■ ' ■' ‘ ' ^^  riSk  r ’i 


^ 90-  r: . • --;fx  vir.;«‘«c^AM  eYXx^<^  dfcijie^  .^0 


Jf'jl 


•:drii 


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- ’.  y ...'•  fc.il  . • .AIL 


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*|!ij' AX^JS;vy_  0^.?  '^jxy  ^ 


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'£^  ‘it£9 


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« yy.*ii*‘ix>xW.ir  4a40-;y^ir<:^it jMoiJO'-'-:  ;3 

►n  ’ .»*.  ' ' '!>■>.  > ' .,  . 

r5j;3X:^i^^^  £>WS^‘t ■^^«ijOXw:^Xqf  ‘ .f. 

^4*!^oX'  . t . 4jLiX^Xa<>  /'  B<t/t  'oi^X'zoiii4'^%L\ 

y ’'  , :•  ■•'>  . J'/  * 'V»''*  : ■■,  .,'  ’' * ■'■■  v-0^ 

t C7 ;0«>Xo4o 


\t 


.'  r X^Z^tXf"  JXo^i 

•^  ■ V.  - . ia  ‘X.h  PP  ^ R , . ' ^ ' ', 

: a tu  p4v  io 

>fV  _ -^'ii'  '~' 

P..TfI,i.t0  :,.'i  ae’JWi^'  «flvj-  %c  nb^ia'o*  ."  , 

I'  r Avu^n  ii'  1 


* ;aaf-  . 

lit: - . ' “ " ..  '■^-  /’,*'  ■^'  /^u 

* , <J‘i«X;f  !<l«  “ 


ii  <1  m't  %^r'  >'.«;■  ^v.v:  ..  - '^m 

' «'  ■'  i]k 


':  :r  ■ .i  ‘»t."i’.^' 

'•  \ - !.  ' .Lff  >f-.'  jf  '' 


15 


is  needed  to  permit  of  any  suitable  decision  amid  such  a maze 
of  possibilities. 

Bromine  and  iodine  are  elem.ents  less  negative  than 

chlorine  and  consequently  would  be  expected  to  have  less 

an 

affinity  for  combinations  with  ( i i . " . element  such  as 
hydrogen.  Iodine  combines  partially  with  hydrogen  at  bright 
red  heat  to  form  an  equilibrium  mixture  in  the  reversible 
reaction: 

Hg  + I2  2 HI 

the  amount  of  combination  or  decomposition  being  readily 
Influenced  by  a change  in  temperature.  Prom  this  it  is  readily 
seen  that  higher  temperatures  accelerate  the  reaction  of  iodine 
with  hydrogen  in  both  directions.  On  the  other  hand,  the 
influence  of  light  is  to  accelerate  the  reaction  in  but  one 

direction  that  which  favors  the  decomposition  of  hydrogen 

iodide  into  its  elements.  Lemoine^*^  reports  that  a gradual 
decomposition  of  hydrogen  iodide  is  readily  brought  about  by 
exposure  to  sunlight  at  ordinary  temperatures,  the  blue  and 
the  violet  rays  being  most  effective.  The  same  author  claims 
that  no  combination  of  hydrogen  with  iodine  was  observed  in 
sunlight  at  ordinary  temperatures;  neither  was  there  any  evidence 
of  decomposition  when  a sample  of  pure,  dry  hydrogen  iodide  was 
kept  in  the  dark  for  a long  period  of  time.  Bodenstein^®  has 
made  the  Interesting  observation  that  the  photochemical 
decomposition  of  hydrogen  iodide  proceeds  as  a monomolecular 
reaction  while  the  thermal  decomposition  is  obviously  a reaction 


cai:-  - J^-^M  « -3ri>^  ja. ■ ■ ,iagV^^  .L:»..k-^  ^ fr%> • 


^ ; ■ 


■ 'V.\'  ■ "',  , ?;  w .•  jh 

^ /i6jt>k  r>i,’ f iii-l  fi-^aoC.  ••,Cdhw.Eik^^^7W  tt  )»' 


‘V-.. 


■J  '• 


■ /' 

i 


* . 


( 

f.c 

i 


-V 


■ V ' ■ ■'  ■; 

lTi4A\^  **'  ' ♦..'<^Ar!  sr'^f  ri>ff«.  aia*-f>'xn\'-a^i6Kj^^  r*ftXxQrtr'^ 

!.«'-■/  •v>*.  r.t  i#»9i':vit,  ■£>£•:  > , - :j!^ 

■-  • ; j_.  ■ ■*»■  n'  ™ ■ 


h' 


♦ Si 


f 


ml^  I rioj^j  iiA  te  ! 


M) 

, i 


■'*^'' . Jii^ 


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> i 


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r 


<w 


•W 


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rt  y.  Hjtrt*  f:<y»’v  .“X-  ; t qK‘'3[iiai{'o  ja  xcf 

r*.  ^.A  •:*♦ 

•j$(  , i i.r.'  tt<A^!  iijiimot  if  :-:J4  ;v'^],<{is 

e.  r ‘'^ 

, jftxi 


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IV, 


’ n:  ;j«tf  .*♦,.  o 

i•^i«e^i;‘■  OT.,'?  '•  ■•;.?  ^ ;g 

:aey  avlf  - 1 ^ Vit^(  ,Vji  ’,ji  jldxf# 

' ■■  ^ V'  •'»■  ■' t **  '' 

i ' - '■  \^.  ■'  ■*.  r;r-..»  '■  , • . '.‘.Ah..-  ,.  ■ 


16. 

of  the  second  order.  Bromine  though  resembling  iodine  in  mg^ny 

particulars  shows  some  decided  differences  in  its  behavior  with 

hydrogen.  For  one  thing,  the  direct  combination  of  bromine 

with  hydrogen  at  red  heat  is  not  a reversible  reaction.  Newth®^ 

shows  how  to  prepare  pure  hydrogen  bromide  by  passing  pure 

hydrogen  saturated  with  bromine  vapor  over  a coil  of  glowing 

platinum.  According  to  Bodenstein  and  Lind^^  the  combination  of 

hydrogen  with  bromine  goes  to  completion  at  224.7°  to  301.3° 

fil 

Centigrade.  Kastle  and  Beatty  report  that  a slight  union  of 
these  elements  occurs  at  100°  C.  in  the  light  and  that  practically 
complete  combination  is  effected  at  196°  C.  in  sunlight.  They 
also  make  the  statement  that  no  combination  of  hydrogen  and 
bromine  was  observed  on  heating  the  mixture  at  196°  C.  in  the  dark. 
In  contrast  to  hydrogen  iodide,  dry  pure  hydrogen  bromide  shows 
no  evidence  of  decomposition  on  exposure  to  sunlight  at  ordinary 
temperatures^^>®^.  However  a qualitative  decomposition,  though 
not  a combination, of  both  hydrogen  iodide  and  hydrogen  bromide 
by  means  of  ultra-violet  light  is  reported  for  the  case  of 
ordinary  temperatures.®^.  From  analogy  with  chlorine  we  would 
expect  any  photochemical  reaction  involving  bromine  or  iodine 
to  depart  from  the  Einstein  Law  by  a wide  margin.  In  this 
connection  it  is  interesting  to  note  the  work  of  Fraulein  Pusch®® 
who  working  under  Nernst  claims  that  the  photochemical  bromination 
of  several  hydrocarbons  in  sunlight  takes  place  in  such  a way 
that  the  amount  of  reacted  products  corresponds  to  but  l/l,000 
to  l/l0,000  of  that  which  should  be  realized  from  the  amount  of 
radiant  energy  absorbed  by  the  system.  Some  years  earlier  than 


F 


%’  ,fT 

I 


'•V 


'Xi.'tr 't  •■ 


i »w  «.  Coil  ■• 


»1»T*  id  *■' 


ur  f 


. ^'Oj 


r,  I 


/nAfri»jflei  .■  >wri  i*v 


;viv,  ^>-■'1^04' 


«U' 


!* 

. ^ 


17. 

this  Nernst^^had  shown  by  calculations  from  his  heat  theorem 
that  the  combination  of  hydrogen  and  bromine  by  the  action  of 
light  would  necessarily  be  of  very  limited  extent.  Assuming 
that  the  mechanism  of  the  reaction  in  this  case  is  similar  to 
the  case  of  chlorine  and  hydrogen,  he  shows  that  the  second 
step  in  the  process  would  be  endothermic  according  to  the 
equation; 

Br  + Hg  — ^ HBr  + H - 15,000  cal. 
and  that  unless  the  system  received  heat  energy  from  the  outside 
the  reaction  would  not  occur.  A comment  on  the  possible  photo- 
chemical reactivity  of  bromine  is  made  by  Lind®*^  who  says,  "It 
is  well  known  that  a mixture  of  hydrogen  and  bromine  is  not 
light  sensitive  at  ordinary  temperatures". 

Prom  the  above  discussion  it  is  seen  that  the  observations 
made  by  various  authoritive  investigators  on  the  action  of 
bromine  to  light  are  in  themselves  quite  contradictory  and  that 
an  acceptable  explanation  for  the  photochemical  reactions  of 
the  halogens  is  still  lacking.  Of  particular  interest  to  this 

go 

problem  is  the  work  of  Coehn  and  Stuckardt  ° on  the  action  of 
light  on  the  formation  and  decomposition  of  the  hydrogen  halides. 
These  men  put  the  pure  hydrogen  halides  of  chlorine,  bromine, 
and  iodine  into  flasks  of  quartz,  uviol  glass,  and  Jena  glass 
and  subjected  the  flasks  and  contents  to  the  rays  of  ultra- 
violet light  for  periods  of  time  sufficient  to  produce  equil- 
ibrium. Their  values  obtained  for  the  decomposition  effected 
in  each  case  can  be  best  expressed  in  tabular  form; 


"n.. 


.r* 


i‘ft.  w 


" r "^  * ’ ( I r * ' •'  y jyM  » . IV.  • 

c^<.  -.'it  :, it  ■••;;  ■ wx/v. 

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c rt(.  t.-siL-Mi^i'  iiKJi  (iti^d't^^ 


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. m 

l>inuotlb  evvxcf»'.‘v0fll;’ 


tJuXvicf>v':^nt^r  i/i»£f.j  /.»e3iE  #I  »tX  iit  Xa«.tjoip  ^ 

- ' ■■'.  ‘’i  ^ . V> 

7-  i-tajoii  f>^j  ito  »'T''i»Bjit>«*v.*u  «Tfc?i»a£5}af.'tf«0vt?*«*'  -vai#' 


vr 


f*- '•  ”-..  * " , •,(*; 

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* ’•  , ' _ *•  '',.<.:?f>,  I'v^  T'V  J'^j^'^  i 

'■L.  lij'  ’ AT  '.^|L»  _*.  -9i.'  i Si.  ‘ - ■•  .' 


4 j T'  % ' ' ’ '‘''’'‘l'  ^ ' I . •••]  M 

1V-.  1'..  '.:  '■■' 

• 

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— ■ ■ ■ ■ ' 

\f. 


J.,'?TE' 


'*'^5 


1^4, 


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m;»Si:'  - f ' 


:X 


7:^1  -■¥. 


18 


Percent  Decomposition. 


quartz 

uviol 

Jena 

>p^220/y/ 

A^254/w// 

SOOyiy/ 

HI  ...  . 

• • 92.29 

. ♦ 100  . . 

. 100 

HBr  . • • • 

• • 100  • 

. . 20  . . 

. 0 

HCl  .... 

. . 0 . . 

. 0 

The  differences 

in  the  effects 

on  the  same  gas 

were  ascribed 

as  due  to  the  selective  action  of  the  range  of  wave  lengths  w 
which  were  able  to  pass  through  the  walls  of  the  flasks. 

Similar  experiments  on  the  formation  of  the  halides  from 
equivalent  mixtures  of  hydrogen  and  halogen  were  tried.  The 
amount  of  corribination  effected  in  each  flask  checked  the  decompo- 
sition percentage  exactly  to  give  the  same  equilibrium  mixture. 
The  authors  make  no  direct  mention  of  the  temperature  conditions 
affecting  the  flasks  during  the  reaction  period^ though  a causal 
reading  creates  the  impression  that  all  reactions  took  place  at 
room  temperature.  This  is  the  assumption  made  by  the  abstractor 
in  a later  journal.  However  a description  of  the  ultra-violet 
light  apparatus  used  here  is  given  in  an  earlier  article  by 
Coehn  and  Sieper®^  in  which  it  appears  that  the  reacting  vessel 
is  entirely  surrounded  by  the  mercury  arc  in  such  a way  as  to 
receive  the  full  heating  effect  of  the  lamp.  In  this  article 
mention  is  made  that  the  temperature  within  the  field  of 
illumination  was  usually  at  240°  Centigrade.  From  this  it 
seems  quite  possible  that  Coehn  and  Stutgard  have  really  measured 
the  thermal  equilibrium  of  their  reactions  after  any  possible 
photochemical  effects  have  taken  place. 


' «»_•  . 

' /• ' 


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19 


III.  EXPERIMENTAL  . 

Part  1. 

As  already  stated  on  p.ll,  the  purpose  of  this  research 
was  to  study  the  influence  of  heat  and  light  on  the  action  of 
bromine  and  iodine  on  hydrogen  and  to  differentiate  if  possible 
the  effects  due  to  each  of  these  agents.  The  first  part  of 
this  Investigation  was  a qualitative  experiment  to  obtain  some 
idea  of  the  action  of  ultra-violet  light  on  bromine,  A clear 
quartz  flask  of  about  200  c.c.  capacity  was  filled  with  a mixture 
of  hydrogen  and  bromine  by  means  of  the  same  apparatus  described 
later  in  Part  2 (Plate  I.)  which  was  used  for  filling  the  Pyrex 
glass  tubes.  The  hydrogen  ?/as  in  considerable  excess,  there 
being  just  about  enough  bromine  present  to  give  a perceptible 
color  to  the  flask.  This  color  could  be  best  observed  and 
roughly  estimated  by  sighting  through  the  flask  to  a sheet  of 
white  paper  held  up  against  its  side.  The  ratio  of  bromine  to 
hydrogen  was  about  one  volume  of  bromine  to  six  or  more  volumes 
of  hydrogen.  This  flask  was  first  exposed  at  room  temperature 
to  the  ultra-violet  rays  emitted  by  a mercury  vapor  lamp.  The 
lamp  and  flask  were  both  enclosed  in  a large  light-proof  box, 
the  flask  being  set  below  the  lamp  at  a distance  of  about  twelve 
inches  in  such  a way  that  it  could  get  a good  intensity  of  the 
light  and  still  be  reasonably  unaffected  by  the  temperature  of 
the  lamp.  In  addition,  a slight  current  of  air  was  maintained 


Ar.l  r-Ai 


1th 


r_  u ^-"i^ 


...n 


; '-  S ^ S /jr*? 

„ ‘ . *,  • . ’M 

p^r^X'iicr  *'*c  v'*-«i  /t.5  ^ •'  j 4<^ 

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</«rM'fuv  f^.:fi  'V  tiri  cit.  anUrtn^l'i:*  ef./iXcv  J?',vW-  Jj/ciTft 


.'<■}'■  jf/o-t'}- ,/\  aX  it3iirAe>^ 


fl^'  V ^ ig  •'"  *ljw7'  ' 

Jhk'\  , i’V  -’  «•  ,;  I ‘ . .yy  ’ vr  ■ ‘ "j^jip 

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V Ji'' ' ■*  • '.•^MliWlfi  ‘ •■:*/ ■*'"  '•■'■■'??■  V 4'*4|| 

V-  ■.&♦-,<' f •«>>;, 5w' 4 ,.  ;•■  •r.-&i.lnm 


iV  !iU( 


".ttatf'.  ,’■  ;.aEifi  ' I ,'■■  ' i’'^  YA  • ' ■ /-■■ 


20 


upwards  by  means  of  suction  to  carry  off  the  ozone  formed  in  the 
box.  This  procedure  incident ly  created  a draught  of  air  from 
the  flask  to  the  lamp  thereby  minimizing  greatly  the  chances  of 
heat  transfer  from  the  lamp  to  the  flask.  After  an  exposure 
of  twenty  hours  no  noticeable  dimunition  in  the  color  of  the 
flask  could  be  observed.  It  is  felt  that  if  any  action  had 
oc cured  it  would  have  been  sufficient  to  have  almost  if  not 
entirely  removed  the  color.  This  view  is  strengthened  when  one 
considers  that  the  total  amount  of  bromine  ?/as  exceedingly  small 
and  that  any  possible  equilibrium  would  be  materially  displaced 
by  the  presence  of  so  large  an  excess  of  hydrogen.  The  flask 

was  then  heated  in  the  free  flame  of  a Bunsen  burner  for  about 
three  minutes  when  the  color  was  observed  to  have  entirely 
disappeared.  That  complete  combination  had  taken  place  was 
decided  when  a sheet  of  writing  paper  appeared  perfectly  white 
on  being  viewed  through  the  flask.  The  flask, now  containing 
a mixture  of  hydrogen  bromide  and  hydrogen,  was  first  allowed 
to  cool  and  was  then  again  exposed  to  the  action  of  the  ultra- 
violet rays  for  another  twenty  hours.  At  the  end  of  this 
period,  the  flask  on  careful  examination  showed  no  evidence  of 
possessing  color.  From  these  two  experiments  it  appears  that 
the  action  of  ultra-violet  light  at  room  temperature  will  neither 
cause  the  combination  of  hydrogen  and  bromine  even  in  the  small- 
est amount  nor  will  it  cause  the  decom.position  of  hydrogen 
bromide  into  its  elements  once  the  compound  is  formed. 


S. 

' .f‘„ 


, •«  , **v-,l^ 


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■'■  ’ - ^ ’ ■'  I '"'  ’ ' ■ j*'""')' ’ ^ ' V* 


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B'A.  ' ■ --  ’ ’ ■ ' ' .X  * ' ■’  : ./ 

• 1.T-  i.C'i^  ^ xii^tr:*uu  ^xf  iixb  ^ ) 

rr,  . ^ * ■ I ' * 1 ■ * * ^ k ^ 

>ft/  ..  ■ ■•■'•■  “ •■  ' • ’;*\  ^'■'‘•*  ■ •■  i%4^  ! 


<y^j  4u^13os  .id:}  va  ai4^)oa  ;t»d(»  i)ap  Xq^o  ■mh)* 

3^  /,3  *i»?^  C’T  ^4-’'  XA  Tc6j^3’0fUJ'’’"W^ 


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t -K  .-f  Ar-  ^ -r-.-i  -- * -*>  ^ .>4  .4  . 


l.  , i,  ’ ' . S ' 

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• ‘ ‘ t.i  !,>'  J-V  ■•■■  "rlv'f.  B?**  ‘■■‘’*■7', 


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■7.'*  :vsj.,aiiJ  .^«i|  .■■ 


21. 


Part  2 

It  was  next  thought  advisable  to  determine  the  influence 
of  temper atiire  on  the  action  of  bromine  with  hydrogen  both  in 
complete  darkness  and  in  the  presence  of  a strong  light.  Here 
obviously  any  difference  in  behavior  could  be  correctly  ascribed 
to  photochemical  effects.  For  this  pxirpose  a number  of  Pyrex 
glass  tubes  1"  in  diameter  and  8'*  long  were  prepared  and  filled 
with  a mixture  of  bromine  and  hydrogen  by  means  of  the  apparatus 
shown  in  Plate  I.  and  described  below; 


Description  of  Filling  Apparatus . 

(A)  is  a U-shaped  electrolytic  hydrogen  generator  filled 
with  a strong  solution  of  potassium  hydroxide  and  provided  with 
pure  nickel  electrodes.  The  generator  was  made  by  bending  a 
large  piece  of  glass  tubing  2"  in  diaraeter  and  30”  long.  The 
current  performing  the  electrolysis  is  controlled  by  means  of 
a lamp  bank  (not  shown)  in  series  with  the  generator.  The 
U-bend  of  the  generator  is  filled  to  a height  of  3"  with  glass 
beads  to  decrease  the  tendency  of  dissolved  oxygen  to  diffuse 
to  the  hydrogen  side  during  electrolysis.  Next  to  the  generator 
is  a tower  (B)  filled  with  glass  wool  to  collect  any  spray  that 
may  be  carried  over  from  the  electrolysis  by  the  escaping 
hydrogen.  Connected  to  (B)  is  a wash  bottle  (C)  fitted  with  a 
tightly  ground  stopper  and  containing  sulphuric  acid  to  a height 
of  2"  to  serve  as  a drying  agent  for  the  hydrogen.  Then, 
following  (C)  is  a tower  (D)  containing  soda-lime  as  an 


f' 


jmm  .:  % . 

- ;u^..  o**>. 


< '» 


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7,  10  JA-rtri  tox/i* 

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’dlA:^  ;>  .,v.  •*Sr3  <l^j(i<i(Cf 

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* ....  _ ^'  'f.  ' 1 ' ' * ■-'**'1;^^ '^■;’’'- 

i-.'i  x^ov!  4in:;,  : »£:xu  (til?, 

■ '-’i ' '--‘  ..,'  •“'.  ,i''  ' " J;jf^  .j|jL 

, ''■  .'■,.  ..^.:\,«i4-;'  >■  >v''^  ■'• , 


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It  jfc.  ''  I 


i ‘j^.  * r,  V.y,.;.a-  - 


22 


additional  drying  agent  and  protection  against  any  spray  from 
the  sulphuric  acid  being  carried  over  by  the  hydrogen.  This 
constitutes  the  system  for  generating  and  drying  pure  hydrogen 
for  the  experiment.  The  hydrogen  was  generated  continuously 
but  was  drawn  over  the  liquid  bromine  and  into  the  reaction 
tubes  intermittently  as  will  be  described  later.  The  remainder 
of  the  apparatus  is  made  of  Pyrex  glass  tubing  one-half  inch  in 
diameter.  The  hydrogen  generating  system  is  made  of  soft  glass 
and  is  connected  to  the  second  part  of  the  apparatus  by  a piece 
of  soft,  tight-fitting,  black  rubber  tubing  (a).  The  bromine 
is  contained  in  the  short  U-tube  (E)  which  immediately  follows 
the  rubber  connection  (a).  (P)  is  a large  U-bend  12”  high 

which  serves  as  a trap  for  any  bromine  carried  over  while  the 
apparatus  is  being  washed  out  with  hydrogen  and  later  serves 
as  an  additional  mixing  chamber  for  bromine  and  hydrogen  when 
the  tubes  (d)  are  being  filled.  The  Pyrex  stop-cock  (b)  serves 
to  isolate  the  tubes  (d)  from  the  rest  of  the  apparatus  when 
they  are  being  evacuated  and  also  controls  the  admission  of  the 
bromine -hydrogen  mixture  to  the  tubes.  The  second  Pyrex  stop- 
cock (c)  leads  to  the  vacuum  line  and  to  a mercury  manometer 
(not  shown).  All  joints  were  of  glass  with  the  exception  of 
the  rubber  connection  (a);  a soft,  tight-fitting  rubber  stopper 
set  in  the  delivery  end  of  the  hydrogen  generator;  and  the 
rubber  tubing  leading  from  the  stop-cock  (c)  to  the  mercury 
manometer  and  the  vacuum  line.  As  mentioned  above,  the  wash 
bottle  (C)  was  fitted  with  a well-ground  glass  joint  to  permit 
changing  of  the  sulphuric  acid  before  each  run.  Every 


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.J./' 


23 


precaution  was  taken  to  exclude  air  from  the  apparatus  during 
the  filling. 


Method  of  Eilling  the  Tubes. 

The  tubes  (d)  were  sealed  to  the  Manifold  (M)  by  means 
of  short  sections  of  capillary  tubing  (e).  The  Large  U-tube 
(P)  was  enclosed  in  a Dewar  flask  filled  with  ice  end  brine 
solution  while  a beaker  of  ice -water  was  brou^t  up  to  the  small 
U-tube  (E)  so  as  to  enclose  it  entirely.  With  the  rubber 
connection  (a)  removed,  about  5 c.c.  of  liquid  bromine  was  run 
into  (E)  from  a pipette.  The  rubber  suet ion- tubing  connecting 
stop-cock  (c)  to  the  vacuum  line  was  disconnected;  the  rubber 
tubing  (a)  was  fitted  in  place;  and  the  stop-cocks  (b)  and  (c) 
were  then  turned  so  as  to  give  access  to  the  air.  A current 
of  3 to  4 amperes  was  sent  through  the  electrolysis  cell  (A) 
and  hydrogen  gas  was  allowed  to  flow  through  the  apparatus  for 
about  two  hours  to  displace  the  air.  This  procedure  was 
expected  to  remove  practically  all  traces  of  oxygen.  The 
U-tubes,  (E)  and  (F),  were  kept  cold  in  order  to  reduce  the 
vapor  pressure  of  the  bromine  and  prevent  loss,  as  well  as  to 
avoid  the  presence  of  objectionable  vapors  in  the  laboratory. 
Some  of  the  bromine  was  carried  over  from  the  bend  (E)  but  was 
readily  solidified  in  the  cold  tube  (F)  and  caused  no  incon- 
venience . 

After  the  apparatus  had  been  thoroughlt  washed  with 
hyc3rogen  the  cold  baths  were  removed  from  around  (E)  and  (F) 


Sv  * 


T>- 


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^ I??.; 

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7^or 


- . r ’tUc^  *t^  <5/  ) 


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. . ; cuQdji  i ( 

‘ I • ’ 

j-iiti-oi  . '(Orfdrii  «tfr  ■■  .^»-iitt5^«  .-■'*■»:  -(alte'f , ^ 


’jf))  (cil  i^'-'“-i'-^  tC,  \iki^9--^i't.  ■|'*! 


5^4 

tfT , 


.f.V  otr  Vi-,  * f in-.|-: . ah  fSp}A;k-  -^S^'  i 

ffPO  aiCAJtvt^.^ic-Xo  xSpiif^tt^  Jftr-ir  i>  oi  ^ ^ 

'.  ''I',  r 3 '■  .'■ 


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«■•  V Vi./,?50r<c;  ;lir.  ,'^iii  ’v-..  lioni<;rthy.t  IflUti^-  P:,] 


;w<ii, 

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/ — ’<■  -j  .-  _'  . f.of  <’,-j\  "'V  ' *• 

- Oit  Q-j  , tq^  afl't/cii  “‘  ^ '■'■  * 

V/  , i , '.< 


ir 


■ j ^ * *1  ■ "J  !*  I*'  I 

ss.y  '.1  (2l>  ra»41  mijtbnd  «i; ' 

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24 


acuum  PLATE 


9 


25 


and  replaced  by  baths  of  warm  water  of  varying  temperatures. 

This  raised  the  vapor  pressure  of  the  bromine  causing  the  stream 
of  hydrogen  to  become  more  highly  saturated.  It  was  fairly 
easy  to  regulate  within  rough  limits  the  ratio  of  bromine  to 
hydrogen  in  the  flowing  mixture  by  setting  the  temperature  of 
the  baths  to  afford  the  desired  vapor  pressure.  After  a suit- 
able wait  to  permit  temperature  equilibrium  to  be  established 
throughout  the  system,  the  stop-cock  (b)  was  closed  and  the 
vacuum  line  and  manometer  were  immediately  connected  to  the 
stop-cock  (c).  This  procedure  caused  two  effects  to  take  place: 
first,  a head  of  hydrogen  immediately  began  to  build  up  in  the 
apparatus  on  the  side  of  the  generator  causing  a difference  of 
levels  in  the  potassium  hydroxide  solution  used  as  electrolyte; 
second,  the  reaction  tubes  (d)  became  rapidly  evacuated  as 
could  be  observed  by  noting  the  mercury  manometer.  About  150- 
200  c.c.  of  hydrogen  was  allowed  to  form  above  the  solution  in 
the  generator.  The  stop-cock  (c)  was  then  closed  and  the 
stop-cock  (b)  opened  cautiously  to  permit  the  bromine -hydrogen 
mixture  to  be  drawn  into  the  tubes.  This  was  the  most  important 
and  delicate  part  of  the  procedure.  Since  the  capacity  of  the 
tubes  was  greater  than  the  amount  of  hydrogen  that  could  be 
safely  accomodated  over  the  potassium  hydroxide  level,  it  was 
necessary  to  be  particularly  careful  not  to  create  a partial 
vacuum  in  the  hydrogen-generating  system.  This  error  would 
cause  air  to  diffuse  into  the  apparatus  through  the  rubber 
tubing  or  through  the  rubber  stopper  and  might  even  cause  the 
solution  of  potassium  hydroxide  to  be  drawn  up  through  the  exit 


r 


''  VttAKr^'K'IIHM 


E. 


:»o 


,*»  Wm^r. 

.eeT.'r  -.„i,.i%^f  'bMv^v  ^O,  •tfl^**  ^TUnf  'io"  erfi*?i  x^,,Of>9>I^W 
t:  ^ 'tiv*  «Ai.tniO'r(>  CfifJ"  iLtj  jA*iurni<t^(i  ’WsqitVi 


V.  ■•t  *■-''■■'  ' ’■‘■ 


'"*tf  « 


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/tti  Vc^  ^ A*iiifroXV><i:<  ai 

- .X^ti  -•  r t'-¥  * . a!B'£'7  %ui  p*iQXX&  '[q^  ^ 

'^r..'^  . -E«  >>.-  r'  ■%  in  t t'f  f¥<etT.f  I-  .^i\  Anr;  iiMill>  4k  ’■-  **-  ■ ■ «i  ^ 


!*:,  L -t  6fi;3Jo  ttAV/  irf)f  *‘r^. 

■ . • 'I-  ■ ';w  '>'■:  ' '•  _ ' %h 

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i...  . .-  • ■ ■■  M.  . 

f » » ■ _ J A 4k  A 4 . J ■ . » 


C4r  e’-Xifipfi-o'JL . «.t4t  . , ii 


,t>9  tosrf,  V.a#iii- 


•«1J  nf  s'i.  I'tii-d  Oi#  rji^e--^  t.^l•^J^ie<ite^^l  rX’?fiC’T^,  . 

ji^..  . ..  . ',.  ■■  . ‘ V ■•:^.^''v.v.^  . ■ '.' 


•'.c  fl  ^s~Ji\uPKt 

to.-'  ^Tir£AiiitLf>  at  Tfai  Aiif  as  V^  !‘a  fJii^^  ,»£ 


' 4*  • . . ^-  ■ . \ . - •„  \ - 

■f  > . .......  . , . . _. 


I 


f 


, K -^tiorik  r-rc/b^tw- od 

cl  %f(j  mo't  6vT  b^w»^ti  1 a'lAr  rs«^g>'ij£)tri  .<»»?’ 

ifd''  iKk >60aX*  n&dtt  fwijw  .(o) ocf^  'f 

*fira'Tjy4/«5l 

^4  .1 . .c^^t4 ' fiwaHiti  ^ ecf  af  _ wijtSl® 


• . 


CLOU  ^ UH-9 


Jf^j  %c  T4i&Av|A6*kii':f  e>o«l^.', ; , >c> 

n . . = ’ '•’  ’ *.  . ' >-'  ''  "'  X’;  ‘!  V’  ■'  ^ 

0>>W  tfl  ,7v'V3irMilXO'tZri^  OV^X^^iJo-7  l^f^i 

D»if-  tfc-rr' 

.■'  . '‘=  . . . '•  .m  ■ 

~iy<!^j  '<crt«  sMiJl  rJt  m 


26 


tube  and  into  the  glass-wool  tower  (B).  To  guard  against  error 

from  this  direction  a heavy,  easily-visible  line  was  drav/n  on 

the  oxygen  side  of  the  electrolysis  vessel  (A)  in  such  a position 

that  when  the  level  of  the  solution  on  this  side  coincided  with 

the  line,  the  level  of  the  solution  on  the  hydrogen  side  was  a 

full  inch  below  it.  Then,  when  the  stop-cock  (b)  was  opened 

the  amount  of  hydrogen  admitted  to  the  tubes  was  just  enough  to 

permit  the  level  of  the  solution  on  the  oxygen  side  of  the 

generator  to  fall  to  the  mark  indicated.  Since  the  oxygen 

electrode  was  open  to  the  atmosphere,  this  procedure  ensured  a 

pressure  of  hydrogen  within  the  apparatus  of  about  2 ram.  of 

mercury  which  was  considered  sufficient  to  prevent  entrance  of 

air  by  diffusion.  Two  or  three  "charges"  of  hydrogen  gas  were 

necessary  to  fill  the  tubes.  The  removal  of  the  last  vestige 

of  air  as  well  as  any  chlorine  which  might  have  come  over  in 

the  first  fraction  of  bromine  was  assured  by  closing  (b)  and 

ly 

re-evacuating  the  tubes.  This  process  of  alternate  filling 
and  evacuating  was  repeated  three  or  four  times.  Both  stop- 
cocks were  then  closed;  the  hydrogen-generating  system  was 
disconnected  ; and  the  tubes  were  sealed  off  at  the  capillaries 
(e)  by  means  of  an  oxygen-gas  flame.  The  tubes  were  then  used 
in  the  following  experiments: 

It  should  be  noted  here  that  the  quartz  flask  used  in 
part  one  was  filled  with  the  above  apparatus.  The  flask  was 
provided  with  a thin  quartz  tube  which  was  sealed  to  one  of 
the  capillary  tubes  (e)  by  means  of  de£ot insky  cement.  The 


‘ T ^ 


"4 


TV. 


. 4lTv,-..„ 

'j  ! "*  *■■  ' V *■ 


erJrt^’K*  » •’♦/•i:-:  c;5r-  ♦ 1 4>S^!#?< < ^.'i 


? ^ ^ ^ £ ©«l»9  V » j t v.XclUi/rXC'  .fjf  V*  I 


il  .'‘il^^lj  r:  j! 


. cri.j’  f#n  <vis;  \o  M/w^t^iidjft  ,«l*^j4S^fi^ 

^.-i  \ •’  ^ .'■'  ■<  ■'■  '■  ‘ ^ 

^ <r  ''  ■ .r,*,  ‘ ' -.  " •',,. 


J i ^ t 


■r: 


C^'  •*•'  t>;.t 


V-  • ' • j 46t?\>-‘'  »rtt  W*'  |3cr  *t«!f^^.Sb] 

. j; 

■ . ‘V".v  ■ 1 ;■■■ ' Va  £ 

.4  >-:'■  ^.  • /»t>0‘i!7*.  !'■  ^.■P  , ',/  3 

**  *"  /?,*•'  ‘ ■''’*!  j«  ’.'■  *’■■ 


V'  ■■  '"•-  ^ ' ' .t,  .*  " ' •'■  "V„  (■''■  "‘'-i  ■'-'’  '■* 

f j?T(jiv«i-«’ X i tMtoJ^)Jit  v^Sirtrr 

-►  ■.'aH»..(.  v^'  . 


.'1 . ' ..  ■ 


t/i  ir  ’X6 


.‘o-'i  i'da  >0  Xa\'CA-^«ftf  A«-,^  .^oiK^d  .>  a%noif  ' 

• ■■•'•  . -.  ■’f  ; 

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f»4/  (^Sf  auJti''.'14.j.^‘.  fi{><XiCiaJ|  »^..*  »iCi>':4u'j;;'"'i:)§  i'rw'^"' ' 

* •>.  ■ < 


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r*  lO^is  *Uc  ■ . -iJLt  J 


a»7  I.  ttP;':»;^^4.^•J<v  ^..  •^■*’uoia.  inaiif-j  4^’ 


i ^ j ♦ 


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v>ii  JX'ua  j- A r.ji,-0  ; 


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■'Si  > i‘  _ 


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. ' - I * ■ . • f.'  '.  ■ ' ' - i*..  Vitf  Vl  v/L^ 

■'»  ,r  ; y] ; af&ife 


> T' 


f '.. 


j^^',;  ^^■ti’ytu  f.taS-t  If'icA 


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« ^ ■ ’%  , _ ■ k i f V,  '/■  •. 


■>.: 


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,.=«-i:7  AAr.*l^"f  ■ '?.  A.  • ■iiiinii  ifflX  ^ :' ',  '••,'.‘>^1.  .7^1.' 54^4-^.  jw.2^Eh^  l..■'^J 


27 


remaining  capillaries  were  sealed  shut  and  the  flask  was  given 
the  same  treatment  accorded  to  the  Pyrex  tubes  except  that  the 
ratio  of  bromine  to  hydrogen  was  made  considerably  less  by  omitt- 
ing the  warm  baths  around  the  U- tubes  (E)  and  (F). 

Results  of  Heating  Tubes 
With  and  Without  Illumination, 

For  heating  the  tubes  a resistance  furnace  was  constructed 
by  winding  eighty  feet  of  #16  Nichrome  wire  around  a section  of 
stove  pipe  18"  long  and  two  inches  in  diameter.  The  pipe  was 
first  insulated  with  a coating  of  bundin' s cement  which  was 
allowed  to  dry  thoroughly.  The  Nichrome  wire  was  then  wound 
carefully  over  thia  layer  of  cement  and  secured  in  place  by 
twisting  the  end  coils  together,  A second  layer  of  the  cement 
was  then  added  over  the  wire  to  protect  it  from  the  action  of 
the  insulating  material  which  was  next  put  on.  An  insulating 
wall  of  "85^  Magnesia"  was  built  around  the  furnace  to  a depth 
of  four  inches  and  allowed  to  dry  thoroughly.  This  material 
has  a high  efficiency  as  an  insulator  though  it  contains  as  a 
binder  some  corrosive  material,  such  as  sodium  silicate,  which 
attacks  metals  at  high  temperatures.  The  furnace  proved 
highly  satisfactory  for  the  purpose  to  which  it  was  put. 
Temperatures  in  the  furnace  were  measured  by  means  of  a copper- 
constar^^Sierrao-couple  attached  to  a milli-voltmeter  graduated 
to  17  milli-volts.  The  thermo-couple  was  made  by  fusing  the 
ends  of  the  two  wires  together  in  a free  flame.  The  hot- 


4''^^ 

..  ' y ■ r- 


. ? ' ■ ' ‘ ' ji '.  .ir  '%• . 


■jy.’ 


/ic^  ' u<4:'.^Xv  >tisrrr^.  xi^TT^  av  :»lf^e'?cu;, ' 


■1»  n 


. Ur  9 ->r 


' •’.  . • ' 0 . , 

*.  ^ . JOl.i'yp*  ^ !^i  '■  • -^‘  ni''  ' 

3fi;v  c^iii  . I ^e«i<.>.Ba  » 


Ul*^ 

> : r •' 


^ ■ ' -2^  .*" 

. wi^rw  *l-0  i ’3*^^' 


-Sijf:--  »e^-  -".i:;x  ^'•>or::K«^j|i  ttpr 


<-:>  /:f  iJtiiiSiVis  -o  To 


fa*  !v?  %ot>.a  c«<*oife  *\  fciite 


-cc.: ‘u-.  «j'7  fUD^'i  .fi  jo©^r>^<:!: 

F'  '**  '*  * V **  'fliS  '***"  "*' 

J ^ ,. , -^O  Ji/n  ^SC  -Mi  , ei^‘ ' 


/v*rr.  .*  t 

•■«  'f' i/ii"  l’'-*X)  -&ppirfJ^P  i'iigtM  #f}j^i(i,Jfil1  ^a.S‘ 

•^>v  •’*■  \,  !■■■;  .'A 

A *^4  >V-.Uitt<^  i^t‘  7c^''/^Uiuh*  rp  .> 


. .,  , kIhB  '‘^'i',''!*  V.*!!!;,  S 


ff.M 


, , ■'■  -*-r  ' ■ ' B 

. -VjM  kiiur.  fl  ' * > ; I 


','■  ''.^f  >.Ci 


28 


Junction  was  enclosed  in  a glass  tube  while  one  of  the  terminals 
of  milli-voltmeter  was  used  to  serve  as  the  cold- Junction  at 
room  temperature.  This  obviated  the  use  of  a second  fused 
Junction  as  well  as  the  need  of  a cold-bath  of  melting  ice  to 
serve  as  the  zero  of  reference.  The  thermo-couple  and  milli- 
voltmeter  were  then  calibrated  as  used.  The  hot-Junction 
was  placed  in  turn  in  the  vapors  of  boiling  water  at  100°  C., 
of  boiling  napthalene  at  218°  C.,  and  in  the  vapors  of  boil- 
ing mercury  at  357°  C.  and  the  readings  of  the  milli-voltmeter 
observed  when  the  thermo-couple  had  come  to  equilibrium.  These 
values  were  then  plotted  on  co-ordinate  paper  so  that  the  read- 
ing of  the  milli-voltmeter  could  be  directly  translated  to 
degrees  from  the  straight  line  obtained  by  connecting  the  three 
points.  The  current  through  this  furnace  could  be  controled 
within  very  narrow  limits  by  means  of  a lamp  bank  and  a plate 
i^ostat  connected  in  series.  About  one  hour  was  required  by 
the  furnace  to  heat  up  for  a given  current  and  to  acquire  a 
constant  temperature.  After  the  amount  of  current  was  adjusted 
for  the  changed  restance  of  the  hot  coils,  the  furnace  would 
remain  at  a constant  temperature  almost  indefinitely.  It  is 
assumed  that  a fluctuation  of  5^  was  possible  during  the 
adjustment  period  and  that  an  additional  error  or  variation  of 
5 more  degrees  was  present  in  the  thermo-couple  due  to  a time 
"lag”  necessary  to  warm  up  the  air  enclosed  in  the  glass  tube 
with  the  hot-Junction  and  to  any  errors  of  calibration.  Although 
it  was  read??y^4o^read  temperatures  on  the  milli-voltmeter  to 
within  two  degrees,  the  temperatures  observed  are  recorded  here 


p 

r 


i 


tyifUU  Wiiil 


‘ 'r  ~ i t i , ' 


: L 


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29. 

as  having  taken  place  over  a range  of  ten  degrees.  Also  since 
a qualitative  comparison  of  the  effects  of  light  on  the  velocity 
of  combination  at  various  temperatures  was  the  information  really 
desired,  the  time  of  heating  the  tubes  was  fixed  at  one  hour* 

In  the  first  set  of  experiments  the  ends  of  the  furnace 
were  closed  tightly  by  means  of  plugs  made  by  rolling  strips  of 
asbestos  paper  into  cylinders  of  the  required  diameter.  This 
reduced  the  losses  of  heat  by  convection  and  served  to  make  the 
furnace  light-proof.  In  the  second  set  of  experiments  one  of 
the  asbestos  plugs  was  removed  and  a 100  watt  nitrogen-filled 
tungsten  lamp  was  brought  up  close  to  the  opening  so  as  to 
thoroughly  illuminate  the  interior  of  the  furnace.  The  two 

sets  of  results  are  tabulated  for  comparison  as  follows: 

Pyrex  Tubes  Filled  VJith  Mixture  of  Hg  and  Brg  . 


(About  three  moles  Hg  to  one  mole  Brg.) 


4 

Heated 

in  the  Dark. 

Heated  in  Light  of  Ng-filled 

Tungsten  Lamp. 

Temp.  °C. 

Observations . 

Temp,  oq. 

Observations . 

Above  265 

Colorless 

Above  270 

Colorless 

255-265 

(Appreciable 

260-270 

(Appreciable 

Ide color izat ion 

(decolorization 

245-255 

/Slight  decolor 

- 245-255 

/Slight  decolor- 

iization 

IjLzation 

230-240 

Paint  color 

235-245 

Faint  color 

Belov/  230 

/no  apparent 

Below  230 

|no  apparent 

{change 

(change 

V 


tj  'Of:. 


K 1 ; 


- f 


I' : 


r r 


' ' = -‘■■‘•^0;  t^/v.i  "fj' 
. ,'CfQ. 

.^o/oo  In  » 


31 


The  arrangement  for  simultaneously  illuminating  and 
heating  the  tubes  is  shown  in  Platell.,  page  30,  An  examination 
of  the  data  given  above,  which  was  taken  from  a larger  number 
of  concordant  observations,  shows  that  the  amount  of  reaction 
occur ing  in  one  hour  for  a given  range  of  temperature  was 
practically  the  same  in  both  cases.  Thus,  reaction  was  initiated 
in  the  dark  at  230°-  240°  and  in  the  light  at  235°-245°;  while 
complete  combination  was  effected  at  about  265°  in  the  first 
case  and  at  about  270°  in  the  second.  The  small  difference  of 
5°  between  these  ranges  of  temperature  is  negligible  in  view 
of  the  limits  of  error  earlier  accepted.  Also,  it  would  natur- 
ally be  expected  that  the  illuminated  reaction  would  occur  at 
the  lower  temperature  so  the  acceptance  of  these  temperature 
ranges  as  practically  identical  is  justified.  In  view  of  this 
experiment  the  conclusion  is  made  that  the  presence  of  visible 
light  has  no  easily  detectable  influence  on  the  rate  of  comb- 
ination of  bromine  with  hydrogen. 

Fart  3 

The  influence  of  Ultra-violet  light  on  the  action  of 
hydrogen  and  bromine  contained  in  a quartz  flask  kept  at 
various  ranges  of  temperatures  similar  in  method  to  that 
employed  in  the  case  of  the  nitrogen-filled  lamp  was  next  studied. 
The  filling  apparatus  described  in  Part  2 and  shown  in  Plate  I 
was  modified  by  replacing  the  manifold  with  a long  glass  tube 


« 

: A ' ' 

fr^  ' ' fM  '^as 

'■  • ■•  • ' ' ■'  ‘ ' -■'^  -*'  V‘  y 'V' 'V  '^fl  ' 4 V'WTi*-  ^ 

6-<'>  W'iSJ^iUi^''rfi'' tiBt«ip(',a.fr^Tj4''»^i  ■ *^Qtj^,j,,^'.j^  (^yj,  i®P'’  lii 

..  ._.  ' . -f  P 


,|  ■neJJPftt*j('c9  ri4  . ■;  aju^  ,..:i'tf*ilt  ai‘ 


?di' ,ggtiitae!l 


j*  L , ■ ' , - "*H  ^ **U  r V ' H 

J s isJauii  tus"^  ».  «*w  ■,,-.y^i' -(tiTijj. 

{ I;  aoltoasr  ia  t.T„vai, 

IT'  •"  -J 


iff 


pi.t/.yi  .i.wa^4.,.i  ,airtr  . 

f a/:f.«  :":V(t?-'‘.;.‘;!.*  .'.>  'f  <hn  m Vt 

..  ^ . ..  i ?.  ‘ ' "5ar.  ^ "V  ' 


^r..JK-'n  c^Tal  ''awj  .V4lsaa  fz  , ,yori?:^w 
la  onii«tyi'St£i  ft.n'ic,  (•n't  , .eivnofw 

aJt  ■ ' 


o r 

U,'.V,;  .4 


- ijii 


■,.''L.f.-  .....  .'?:  - 


pbne;rcr^£.o*  ^*2 


if  is  'XJIOW  ttfyrw 'jW4?4!»m  Mi 

' ■ .«.:?  X '\  “^1 


->6:  - ‘ '* 


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r 


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^,)l 


I,  - ■ .-i»'".^'-r/  ■ .'^'  S'' 

(T  -<t,ioo  jc.-  aJ.li  ,BH.t  .Hk  .^tappVn-.i  oXtlk3-.  r>ats}.  j <if<:  «m 


":  'V  ■■ 

k " 


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r :>!s^4 :' .. 'SSl..  “ fX-t  Xilma 


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.•tff'-OKa?S.u  ftdj  Bc:  .rrtsU  JeJoJv-e-iJftT- I'liv  aoflki'C-fli 

i?!  f ■ ■ . ■■*•  ’•  *'•'  »»Si  '.V^^ 


f 


boi^/itfn  dxoa  8.'»  '^4if,  A<]^:t§qiiro.-. 

iy  ' ■ • ‘ * , ' . -'-  I'^p  .*  . ii:  r'  .-^ 

/■•  iJ'''  V/ 


X uX  m 


IV, 


i^'^rtss-vr  "-r’’Tj'11'wwwi..a.  — . . . y jr‘ Jl 


t t _ ^ 


32 


•d 


PLATE  III 


33 


to  the  end  of  which  was  connected  the  quartz  flask  (H)  hy 
means  of  a joint  of  de  Kotinsky  cement.  The  tubing  was  bent 
so  as  to  bring  the  quartz  flask  into  the  electrically  heated 
oven  (G).  The  light-proof  box  containing  the  mercury  vapor 
lamp  was  brought  up  to  the  oven  so  that  the  ultra-violet  rays 
could  shine  through  a hole  cut  in  the  door  and  thereby 
illuminate  the  interior  of  the  oven.  The  arrangement  of  the 
apparatus  ia  shown  In  Plate  III.  Page  32.  The  quartz  flask 
was  filled  in  the  regular  maimer  and  then  isolated  from  the 
rest  of  the  apparatus  by  closing  the  stop-cocks  (b)  and  (c). 
Two  series  of  experiments  were  then  carried  out  ?n^?fee  flask 
and  contents  were  heated  first,  while  under  the  influence  of 
the  ultra-violet  light  and  second,  while  exposed  to  ordinary 
diffuse  day-light.  The  time  of  exposure  was  still  one  hour 
though  the  temperatures  required  to  obtain  any  given  effect 
would  be  expected  to  differ  from  that  required  in  the  case  of 
the  Pyrex  tubes  because  of  the  difference  in  capacity  between 
flask  and  tubes.  The  ratio  of  hydrogen  to  bromine  was  made 
three  to  one  in  this  case,  also.  Results  are  tabulated: 


Heating  Mixture  of  Hp  and  Bro  in  Quartz  Flask. 


Exposed  to  U-V.  Light. 
Temp.  °C.  Observations. 


Exposed  to  Day -light. 
Temp,  oc.  Observations. 
Above  310  Colorless 


Above  310  Colorless 


295-305  Appreciable 

Decolor izat ion 
280-29©  Slight  Decol. 


300-310 


280-290 


Appreciable 
Decolonization 
Slight  Decol. 


260-270 


II 


II 


265-275 


II 


II 


Below  255  No  Change 


Below  260 


No  Change 


>% ' 


{J.  . •■  ;'• ! 't  :;r 

i J 'v,-  ,•:■;  .•  * *^.{j 


Ovf/a 


j c-iuiv..;  .■'•.ji, 


i.<-'  f ' 


-j  ^ 


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t . 1 

■ • «.i': 

> 

i«TO 

'r'  R I ' / 

; 

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r:. 

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■ “f  - 

■*  V '■  ' ■ t r 

Krr..Kr; 

-’.CJ  >':  *.0’,v 

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vcf' 'j  -.Irnf 

•.j  ■ 

1 . •. 

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■I 


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St/'-?  oV 


34 


A comparison  of  these  values  justifies  the  assumption  that 
ultra-violet  light  has  no  more  effect  on  the  combination  of 
hydrogen  with  bromine  than  has  ordinary  day-light.  If  the 
results  of  Part  2 on  the  comparison  of  visible  light  with  total 
darkness  are  taken  into  account,  one  can  say  with  full  justi- 
fication that  the  combination  of  bromine  and  hydrogen  is  purely 
a thermal  phenomenon  and  the  rate  of  this  combination  is 
determined  by  the  concentrations,  amounts  of  reacting  substances, 
and  the  existing  temperature  conditions_,and  in  no  way  influenced 
by  existing  conditions  of  illumination. 

An  experiment  to  determine  whether  hydrogen^^Suld  be 
decomposed  by  the  agency  of  ultra-violet  was  next  tried.  The 
quart used  in  the  first  part  of  this  experiment  was  filled 
in  the  ordinary  manner  and  then  sealed  off  from  its  quart  tube. 
The  flask  and  contents  were  then  heated  in  a Bunsen  flame  till 
total  combination  was  effected  as  in  Part  I . This  flask  was 
then  put  into  the  oven  (H)  and  exposed  to  the  rays  of  ultra- 
violet light  at  various  ranges  of  temperatures  as  was  done  in 
the  case  of  t he  flask  filled  with  the  -uncornbined  mixture. 
Temperatures  in  steps  of  10°  from  260°  to  the  room  temperature 
were  tried  and  the  flask  carefully  observed  to  note  any  appear- 
ance of  color.  To  the  best  of  o\ir  knowledge  no  indication  of 
the  presence  of  free  bromine  could  be  observed  at  the  end  of  any 
of  the  heatings.  Therefore,  from  these  collective  experiments 
the  conclusion  is  drawn  that  the  inter-action  of  bromine  and 
hydrogen  is  not  an  easily  recognized  photochemical  process. 


* 


' . 


r ^ '^.''Jl 


f'^i 


C-  Orta  '6ol'y(,.tri4b^  .■'■rt:?  >V 

' i\  'lo  m tmid**  ^ 'ijrff  tfo ‘JftorXf  ^•-'^«y«f.\irt 


* ’-d^  \*,  . «4rt  ^ 

\ ^ N M.  , ' '■  i 


■■  ti  <^T‘i-’j*7^X4i iC'u  <-jt.  ^^‘ic 

’*  ■ ' ■ • '■  •*  *‘^-  --rmi'  ■;  . - ’>■ 


»•''■'■’  • “ ’*«  •'  6 ••  '•^.*s«  '«<<^'si»»-*'i »W  «-/f/‘nrf 

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ji'  XCXt  y «It  7«*ijir  «^«vr  «jr,-;^,^ni»Ci' 

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.'  'J 


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> 7''*' ■•■  '4!1,  y 


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ru^x,/:^^‘jtn<Tw:r  «og^  '^r  titf  • *i(?‘.-^t  ^uXt-tr  ,rti'  ^ 

-*X«erJijn  v;x«  njtiff  ^ VtVijMy4t  v.,;^X1l  t*li 


to  j;ii»  ,3iii-  i/j.  5fltvru'<fo  W ^ iW 

A 1 litVr  MAttA  • li.  *’  .<_..  . .■^-  . w„  • : ^ <i4  .*,t  :it> 


. 't  .■  ..  . ■ **  ' ‘^'  .'■  ’ if’ 


i. 


Lt'  4 » ‘ * 

.' 


L . , 


35 


Part  4, 

A recent  article  by  Baly  and  Barker*^^  makes  reference  to 
the  observance  of  a sudden  Increase  in  volume  in  the  case  of 
a sample  of  chlorine  gas  which  had  been  subjected  to  the  action 
of  ultra-violet  light.  Draper  had  also  observed  this  phenomenon 
which  has  been  called  after  him,  the  Draper  Effect.  It  was 
suggested  by  Balyjand  Barker  that  the  volume  change  was  due  to 
an  activation  of  the  chlorine  molecules,  probably  a splitting 
of  the  molecule  as  has  been  postulated  by  Nemst,  and  that  the 
increase  or  activation  was  due  to  the  violet  end  of  the  spectrum 
and  was  independent  of  any  heating  effects*  It  was  decided  to 
try  out  this  effect  with  both  chlorine  and  bromine  in  ordinary 
sun-light  and  to  note  the  comparative  action  of  the  blue  and 
the  red  ends  of  the  spectrum  by  shutting  out  part  of  the  rays 
with  appropriate  screens.  The  apparatus  for  trying  out  this 
experiment  was  made  as  follows; 

Two  glass  bulbs  of  about  200  c.c.  capacity  were  blown  and 
sealed  to  the  two  opposite  ends  of  a long  T-tube  made  of 
fine  capillary  tubing.  The  open  end  of  the  T-tube  was  connected 
to  a chlorine-generating  apparatus  and  an  evacuating  system. 

The  bulbs  were  washed  with  chlorine  gas  by  successive  evacuation 
and  filling  and  the  whole  apparatus  was  sealed  off  by  closing 
the  rem.aining  end  of  the  T-tube  by  the  use  of  a air-gas  flame. 

The  bulbs  containing  bromine  were  similarly  filled  except  that 
the  bromine  was  distilled  over  from  a flask  instead  of  being 
generated.  Also,  all  joints  in  the  case  of  the  bromine  were 
of  glass  while  rubber  connections  were  thought  permissable  in 


i."1 


H 6T 


I'J'-V- 

^ n'n  ’ m 

^ -S.  aw,  'S 

-*t 


■T  i • ' ■ . ' j 'fc*  ^ r 

p.t  J ••■jrt65t^'I  n-.'v'aiS  0''i«uKj»,T  •a'^?,;,#'  .(' 

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.-iia-lq  a-'i.'  f,..Y«f(wdo  oalM'tk-d  -xvi^K^  ' . tisi  I:  T®  iv.iriJ'fo'CP 

' ^ - *•*■:  , •■  V ■T  ■ i 

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> axo  ■;  - X-1.KI  ,f«)  V*/' 

j.^’oltoa  'ftX!  4*.j'--*:  f4^  O’Swfr.jb-jt, 

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c^cc/'to,  ’jiS€»'fertfca£ii!^ 

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5<5XXi^l 


! id  ai^itsn^'  foiob^i 

‘ "^r  T^/!**-'-**  'A*jg‘.g»r’yaBi.T  . ■ 


36 


the  case  of  the  chlorine.  The  bulbs  were  enclosed  in  a light  - 
proof  box  with  a window  cut  in  the  top  for  t he  admission  of 
sunlight.  The  fine  capillary  of  the  apparatus  joining  the 
bulbs  was  made  to  serve  as  the  manometer  of  the  apparatus  by 
the  condensation  of  some  of  the  enclosed  halogen  to  form  a 
meniscus  which  was  very  sensitive  to  any  changes  in  pressure 
between  the  bulbs.  In  the  case  of  the  bromine  a small  piece  of 
ice  served  very  well  to  give  the  bubble  desired.  In  the  case 
of  the  chlorine  use  was  made  of  solid  carbon  dioxide  snow  which 
readily  condensed  some  of  the  chlorine  to  give  a bubble  which 
served  as  the  manometer.  One  of  the  bulbs  was  kept  in  the 
dark  while  the  other  was  ill\iminated  through  the  window  and 
any  change  in  position  of  the  small  bubble  observed.  It  was 
found  that  when  light  was  suddenly  admitted  to  the  bulb  that 
a definite  expansion  took  place  but  that  there  was  no  noticeable 
difference  in  effect  between  the  use  of  the  two  colors  of  screens. 
It  was  hoped  that  the  blue  screen  would  cause  a far  greater 
expansion  in  the  gas  but  any  greater  shift  in  position  by  the 
sensitive  bubble  was  considered  explanabiejon  behalf  of  the 
difference  in  absorption  of  the  two  colors  by  the  two  gases. 

We  put  forth  the  theory  that  the  expansion  of  chlorine  and 
bromine,  too,  when  subjected  to  light  is  due  to  a heating  effect 
caused  by  the  conversion  of  light  energy  to  heat  by  adsorption. 


4 


i 


37. 


IV.  CONCLUSIONS. 


The  combination  of  bromine  and  hydrogen  at  various 
temperatures  and  under  various  conditions  of  illumination  has 
been  studied.  It  has  been  found  that  this  reaction  is  not  a 
true  photochemical  phenomenon  and  that  the  velocity  of  combin- 
at  ion  is  unaffected  by  existing  conditions  of  illumination. 

The  decomposition  of  hydrogen  bromide  by  the  action  of  ultra- 
violet light  has  also  been  attempted.  It  has  been  found  that 
hydrogen  bromide  will  not  decompose  into  its  elements  under  the 
influence  of  ultra-violet  light.  The  expansion  of  chlorine 
and  of  bromine  on  exposure  to  various  regions  of  the  solar 
spectrum  has  been  observed  and  the  theory  put  forth  that  this 
expansion  can  be  explained  on  the  basis  of  the  conversion  of 
radiant  energy  into  heat  by  adsorption. 

Since  it  is  well-kno^wn  that  chlorine  combines  readily 
with  hydrogen  under  the  influence  of  light  and  that  hydrogen 
iodide  decomposes  even  more  readily  under  the  sa^ie  influence, 
this  indifferent  behavior  of  bromine  and  hydrogen  bromide  to 
light  is  worthy  of  note.  The  fact  that  bromine  is  intermediate 
in  position  between  chlorine  and  iodine  in  our  Periodic  System 
is  also  of  interest,  though  the  fact  may  or  may  not  be  of 
special  significance  in  this  connection. 

The  results  obtained  in  this  research  fail  signally  to 


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38. 


agrse  with  the  work  of  Coehn  and  Stuokardt  who  report  a total 
decomposition  of  hydrogen  bromide  in  quartz  and  a total  combin- 
ation of  hydrogen  and  bromine  in  Jena  glass  under  the  influence 
of  ultra-violet  light. 

Similar  work  on  the  combination  of  hydrogen  v/ith  iodine 
and  the  decomposition  of  hydrogen  iodide  in  the  light  is  now 
in  progress. 


39. 

V.  ACKNOWLEDGMENTS.. 


In  concluding  this  thesis  the  author  wishes  to  express 
his  appreciation  to  Dr.  W.  H.  Rodebush  for  his  kind  interest 
and  supervision  in  the  pursuance  of  this  research.  Thanks 
are  also  due  Dr.  Gerald  Dietrichson  and  Dr.  Einmett  K.  Carver 
for  occasional  help  and  personal  interest. 


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